REFERENCE GUIDE FOR OPTICAL MEDIA
Terence O’Kelly

Content Links
1. Frequently Asked Questions (FAQs)
a. Digital audio
b. CD-R recordingc. CD-RW
d. DVD and Recordable DVD
2. Introduction to the Reference Guide
A. Memorex history
A. Differences between analogue and digital recordings
B. Binary number system
C. Digital audio
3. Compact Disc and how it works
A. Book Standards
B. Error correction—CIRC
4. CD-R
A. Recording dyes
B. Music CD-R
C. Reflective surface
D. Capacity
E. Speed ratingsa. CLV and Z-CLV
b. CAV and P-CAV
c. Comparison of speeds vs. time savings
5. CD-RW
A. Stability
B. Speed ratings
6. Mini-Disc
A. Magneto-optical recording
C. ATRAC compression
D. Hi-MD
7. DVD
A. DVD Numbering
B. Recordable DVD
C. DVD Capacities
8. Recordable DVD Formats
A. DVD-R
a. Data addressesb. Land Pre-pits
B. DVD-RW
C. DVD-RAM

a. Data addressesb. Cartridge types
D. DVD+R
a. Data addressesb. ADIP
E. DVD+RW
9. Recording onto DVD discs
A. VR Recording onto DVD--+VR and –VR
B. CPRM
C. Capacities of recordable DVD discs
a. Capacities in terms of timeb. Set-top recorder time chart
D. Double-Layer Discs
E. Recording Speeds
10. Blue Laser Recording
A. High Definition Video
B. Blu-ray versus HD DVD
C. Laser wavelengths
a. Numerical apertureb. Comparison of High Definition Proposals
11. Life-time Expectations of Optical Media
12. Care and Handling of Optical Media

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FAQs about Optical Media
There is a great deal of misinformation, hype, and misunderstanding in the field of optical media.
Memorex wants to help customers make educated choices about the media and formats theychoose; so we have assembled a list of Frequently Asked Questions and the Memorex Reference
Guide for Optical Media covering the subject in detail. Click on the blue text to get to the answer toany question. Some answers will include additional links to the Memorex Reference Guide for
Optical Media for even more information.
Digital Audio1) There’s “analogue” and there’s “digital.” What's the difference?
2) What’s the difference between a “bit” and a “byte”?
3) How can a computer count using just 2 numbers? (The binary counting system)4) How much data can I fit on a disc?
5) How can a computer store and play music?
6) Some people say analogue is better than digital. Others say the opposite. Which is correct?
7) What’s the difference between a “medium” and a “media”?
8) How do CDs work?
9) A scratched CD can still work most of the time. How does a player correct those errors?
10) What do people mean by a Red Book specification?
11) Are CDs and CD-ROMs the same? Why is there a “Yellow Book” for CD-ROMs?
12) My computer drive won’t play CDs. Why not?
13) There are a lot of abbreviations used in talking about CDs. What do these mean?
a. ATIPb. BLERc. CAVd. CIRCe. CLVf. E11
g. EFMh. HDTV
i. MPEGj. MP3k. OPC
CD-R Recording
14) CD-Rs are recordable CDs. How can they record information?
15) I’ve heard greenish CD’s are the best. Is that true or is there a better color?
16) CD-Rs used to be gold; now they’re silver like CD’s. What’s the difference?
17) How much can a CD-R hold?
18) Are 80-minute CD-Rs better or worse than 74-minute discs?
19) What about 90-minute discs?
20) Why won’t some CD-Rs work in my stereo CD-R recorder?
21) My CD-Rs won’t play. Are they defective?
22) CD-Rs are called 12X, 16X, 24X, 32X, 40, 48, and even 52X. What’s the difference?
23) Are faster rated discs better than slower discs?

324) Is it better to record at slow speeds or fast speeds?
25) I have an older drive that records CD-Rs at 4X. I can only get discs now rated at 40X or
more but they sound terrible. Are the discs worse now than before or is something wrong
with my drive?
26) I’m very careful about protecting the bottom of my CD-Rs, but someone told me the top is
more fragile. Is that true?
27) How long will CD-Rs last?
28) I’ve heard that the colored discs are different from plain discs. Aren’t they just painted
CD-Rs?
29) How can a laser read through a black disc?
30) What’s the best way to label CD-Rs and CD-RWs?
31) What’s the best way to store CD-Rs and CD-RWs?
32) I upgraded from a 4X drive to a 24X drive. Why doesn’t the new drive record 6 times faster?
33) My recordings fail due to “buffer underrun.” What does that mean?
34) I have a 32X recording drive, but I can only record at 24X on Memorex discs that are labeled
as 48X. Are these discs defective or mislabeled?
CD-RW35) Now some CDs are erasable. How can they get erased?
36) What do the numbers 32/12/40 on CD drives mean?
37) I bought a 32X CD-R drive before I realized drives could go to 52X. Should I upgrade to takeadvantage of the time savings with the faster drive…or do I run the risk of disks blowing up in
my drive?
38) I bought some 8-24X CD-RW discs that won’t work with my high-speed drive. The drive canrecord CD-RWs rated 4-12X. What’s wrong?
39) I can’t format Memorex 1-4X CD-RW discs, but other brands work. That means these discs
are crummy, right?
40) Will “high-speed” CD-RW drives work with any CD-RW?
41) I bought 700MB CD-RWs, but I can’t put more than half a gigabyte on them. Are theydefective?
42) I have a whole spindle of defective CD-RWs. Every disc fails to format. How can every discbe bad?
43) What’s the difference between “ripping” and “burning”? Or are they the same?
DVD and Recordable DVD44) How can DVDs hold more if they’re the same size as CDs?
45) What’s the difference in a DVD 5 versus a DVD 9? How many versions are there?
46) What’s the storage capacity of a DVD?
47) My DVD player won’t play CD-Rs but it plays music recorded on a CD-RWs! How can thatbe?
48) Now people can record on DVD, but there are 3 different types? Why?
49) What’s the difference between the types?
50) I’ve heard that my home video cassettes will deteriorate in a few years. Which format
should I pick to transfer them?
51) What’s DVD-R?
52) Can I copy rented DVDs onto DVD recordable discs to build my own library?
53) What’s DVD-RW? How is it different from DVD-R?
54) My set-top video recorder can record DVD-RW version 1.1 discs but not version 1.2 discs.
What does this mean? What’s the difference?
55) What’s DVD-RAM?
56) What’s DVD+RW? There’s a DVD+R, too. Does the plus mean it’s better than the minus?
57) Will any of these recordable DVDs play in my DVD player?
58) I have a 52X CD-R recorder. What speeds are there for DVD recorders?

459) I’ve heard that if I use the wrong speed disc in my DVD drive, it can be destroyed? Is that
true?
60) I tried to record a 4.5GB file onto a 4.7GB DVD+RW but it wouldn’t fit. How come?
61) My DVD drive won’t record on Memorex DVDs. Is the quality that bad?
62) I have a choice of CBR or VBR in my video capture. What are they?
63) What are VR formats?
64) I captured my tapes at the highest “MPEG-2 quality.” Why can’t I make a DVD?
65) What is the best bit rate to choose when I capture video?
66) My DVDs don’t look as good as the VHS tapes they came from. Aren’t DVDs supposed tobe better quality than VHS tape?
67) Once I’ve made DVD copies of my camcorder footage, can I throw away the tapes?
68) I tried to copy my VHS movies onto DVD, but they look terrible. Do I need better quality
discs?
69) How many minutes of video can I record on a DVD recorder?
70) What do I need to record video onto DVDs?
71) Which of these formats should I buy?
72) Which is the best format?
73) I have a video DVD recorder that can record at 24X, but a friend says the fastest speed is16X. Is he right?
74) I tried to format a DVD-RW, but I got an error. Now I can’t erase the disc because my drive
tells me it isn’t even there! What did I do wrong?
75) What are the numbers that appear on a disc? Which one is the MID code?
High Definition Video76) What is high definition video?
77) How do I get high definition programs?
78) I’ve heard that blue lasers are coming. What does that mean?
79) Why are there two different high definition discs?
80) Which disc is better, HD DVD or Blu-ray?
81) Can I play high definition DVDs in my DVD player?
82) Will the new high definition DVD players be able to play my old DVDs and CDs?
83) Will Blu-ray and HD DVD be compatible with each other?
The answers to the questions follow below. Click on the link to the Memorex Optical Media
Guide to get more detailed information, including pictures and charts. If you have a question
not listed in our FAQs, E-mail the question to us; and we will add answers to the mostfrequently asked questions.
Digital Audio
1) See the Reference Guide for Optical Media section “Analogue vs. Digital.”
2) A “bit” is a binary digit; a “byte” is a digital word of eight bits. (Reference Guide)3) The computer uses a binary counting system instead of our usual decimal system.
(Reference Guide)4) Reference Guide, Figure 1.
5) Reference Guide, “Digital Audio.”6) Digital audio sound is not perfect. Nothing is. But the distortion, noise, and mechanicalconcerns of CDs, for example, are far less than that of other popular media. For example:
a. Distortion is many orders lower on a CD than on an LP or a tape.
i. An LP has “low” distortion at only 2 points with regular tone arm geometry.
ii. 3% Harmonic distortion or saturation defines a tape’s highest record levels.
b. Dynamic range for a CD is above 90 decibels and uniform across the disc.
i. LP S/N ratio is low and worsens toward the end of a record.
ii. Tape needs assistance from noise reduction circuits to overcome hiss.

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c. Noisei. The LP has pops, clicks from debris or damage in the groove.
ii. Phonograph tables suffer from rumble noise.
iii. Tape has bias noise, modulation noise, DC noise.
d. Mechanical alignment problems and alignment issues.
i. Wow and flutter for both LPs and tapeii. LP stylus height, overhang, anti-skate, tracking force, resistance/capacitanceiii. Tape head height, zenith, and azimuth alignments and torque adjustments
e. Weari. The stylus wears the groove in the LP; the stylus itself suffers from wear.
ii. Tape heads wear; there are magnetostrictive effects on some tapeformulations that reduce high frequencies; rub-off of oxide/binder
The CD is not a perfect medium, but it will sound more like the original recording in a far
wider variety of playback systems than either a vinyl LP or a tape cassette possibly could.
7) A “medium” is the carrier in the middle between a source of information and its intended
audience. TV is a medium. A CD-R is a medium. The word is single. More than one
medium are “media,” the plural of medium. TV is one news medium; TV, newspapers, andthe radio are news media. Almost no one in any media business, whether news or discs,
ever uses the words correctly.
8) Reference Guide, “How a CD Works.”
9) Circuits to identify and correct expected errors are built into CD players and drives. See thehighlighted Reference Guide section for a detailed, but not too technical explanation.
10) The Red Book is the book published by Philips defining digital audio discs.
11) Although they look the same, the information on audio CDs and CD-ROMS is arranged
differently. See Reference Guide section discussion.
12) The CD drive in the computer probably has no audio software to identify and support the
playback of audio CDs. It only recognizes CD-ROMs with data. It may be necessary to add
audio software and even a sound card to the computer to get it to play music.
13) Abbreviations:a. ATIP
Absolute Time in Pre-grooveb. BLER
Block Error Ratec. CAV
Constant Angular Velocity
d. CLV
Constant Linear Velocity
e. CIRC
Cross interleaved Reed Solomon Codef. E11an Error with 1 bad byte corrected at C1 stage
g. EFM
Eight to Fourteen Modulationh. HDTV
High Definition Televisioni. MPEGMoving Picture Experts Groupj. MP3
Motion Picture experts group layer 3
k. OPC
Optical Power Calibration
CD-R Recording
14) See Reference Guide, “How a CD Works.”
15) The color of the CD-R is a combination of the dye used and the reflective mirror layer behind
it. Different dyes have different characteristics, but there are many more important factorsthat determine the quality of a disc than the dye and its color. See Reference Guide, “CD-R
Dyes.”
16) The reflective layer of a CD is aluminum. That metal would not work with the corrosive dyesof CD-Rs, so manufacturers used gold at first and then generally switched to silver or silver
alloy to reduce costs. See Reference Guide, “CD-R Reflective Surfaces.”17) The maximum safe level is 80 minutes of audio or 700 MB of data (before formatting).
Reference Guide, “CD-R Capacities.”18) The question is not whether one is better than the other, but whether or not the discs are
more or less interchangeable with players and drives and the data are retrievable. 80-minute6

discs push the limit of the specifications, but that is not a problem with modern players anddrives. Older CD players, car players, and older drives are more likely to have trouble with
80-minute discs than with 74-minute discs. See Reference Guide, p. 13 for more details.
19) 90-minute discs can be recorded and played in very few drives. There is little software
support for this capacity, and it can actually pose a danger to drives not designed for“overburning,” that is, going up to the outer edge of a CD-R. Increasing the capacity requires
violating the specifications for track pitch and pit size and writing in areas intended for otherinformation. Even if a drive could manage fitting 90 minutes of audio on a CD-R, there is no
guarantee that all CD players would be able to recognize or play it.
20) Stand-alone stereo CD-R players are called “digital audio disc recorders.” They require CDRs that have a special code in the ATIP section that identifies them as DA or “digital audio”
discs that can only be recorded in these types of recorders. Computer drives can use either
standard or DA media, but DA recorders can only record on DA discs. Once recorded, theDA discs will play no differently from any regular CD-R. Only the recording process is
restricted, not playback.
21) If the CD-Rs won’t play in the drive that burned them, there is something wrong with themedium, the drive, or the recording software. If the discs do play in that drive but not in
another player, the reason could be an incompatibility with the reading laser and the disc.
Although there are tight specifications for media, there are very few specifications for drives.
Older CD players sometimes have trouble reading CD-Rs for a variety of reasons includingreflectivity, pit geometry, or groove shape on the disc or tracking problems in the drive.
Newer players and drives have far fewer problems with compatibility.
22) The number rating of discs is a measure of how fast they can be recorded in a drive rated tobe capable of that speed. A 16X disc can be recorded at 16 times normal speed (“Normal” isthe playback speed of a music CD, or “1X.”) in a drive rated at 16X, but at only 8X in a drive
rated only for 8X maximum. A 24X drive, however, might try—and succeed—to write to a
16X disc at 24X; but if it has trouble, it will drop down to a 16X speed. See Reference Guidefor some interesting details on what the speed ratings really mean.
23) Faster discs have thinner dyes that react faster to the laser light and the greater laser power
used. There is no quality difference in this regard, although discs rated at the highest speeds
have to have excellent balance, concentricity, and uniformity so that they do not cause
problems for high speed drives. These are lesser concerns at slower speeds.
24) There are many opinions from experts who claim they can hear differences in discs recorded
at 1X and those recorded at faster speeds. That is unlikely, but any measurable differences
would be due to the design of the drive and the condition of the laser and their compatibility
with whatever medium is being recorded. The facts are: a) recording lasers pulse at slower
rates at slow speeds but act more uniformly at higher rates of speed; b) more power isrequired at faster speeds, but the increase in required power is not proportional to theincrease in speed; there may actually be less drift in laser power at the faster 4X-12X speeds
and beyond; c) lasers in drives operated at the maximum speeds all the time will age fasterthan if they were used at a lower power levels; d) slower speeds will cause vibrations at lower
frequencies which may interfere with the transfer of data: faster speeds create vibrations at
higher frequencies that may pose less of a problem; e) tests measuring error rates find little
difference in results at slow speeds or high speeds, but higher speeds often show a veryslight advantage.
25) The latest discs available today are designed to be recorded at speeds of 48X to 52X. Older
drives that record at slower speeds work best on CD-Rs with slow acting dyes. Unfortunately,
just as computer operating systems and peripherals are always being updated in favor of thenewest and fastest products, the same is true of CD-Rs. Fast reacting, high-speed CD-Rs do
not work as well with the old, slow CD-R recorders. The poor sound quality is due to the drive
overburning the fast acting dye and distorting the pits. Although there is nothing wrong witheither your drive or the new discs, they are no longer compatible. One either has to find old
CD-Rs or upgrade to a faster drive that can handle the new discs.

726) The laser looks through the bottom of the disc, a solid piece of clear polycarbonate plastic.
That plastic is sturdy but should not be scratched or soiled in a way to interfere with thepassage of the laser’s light beam. The top of the disc, however, is only a coating of lacquer
covering a thin deposit of reflective metal. It is very delicate. Never write in the top of a discunless one is using special pens designed for CD-R writing. The wrong type of pen (aballpoint pen, for example) can either damage the surface and the data below or use inks
containing acids that will damage the lacquer protection.
27) The lifetime of a CD-R is estimated by environmental tests that try to simulate theaccumulation of damage from light, heat, humidity, and exposure to the normal chemicals in
the air. The “death” of a CD-R is defined as the point at which the number of errors
accumulates to such a degree that simple error correction can no longer retrieve the data on
the disc. Different dyes as well as different manufacturing skill and techniques haveproduced discs estimated to last from 70 years to over 100 years, far longer than the
playback technology will last—or even the lives of the owners. The assumption is that thediscs are properly handled and stored away in the dark over that time period. Real-life
conditions suggest that careless handling and heedless exposure to sunlight can ruin a discin a month or less for poor quality discs.
28) Colored discs are very often just silk-screened with ink in various shades, but Memorex’s“Cool” discs are actually colored clear through. There is no difference in performance withthese discs because although we humans see the full spectrum of visible colors on the discs,
the laser has a much narrower vision restricted to 780 nanometers of wavelength. The only
color that poses a problem for a laser is green because green can absorb the red laser light.
(Experiment: put a green mark on a piece of paper and shine a red light on the paper. The
paper looks green, but the mark appears black. It absorbed all the red light.)
29) Same answer as above. To human eyes the black disc appears to absorb all “visible” light,
but it will not absorb the very narrow range of the red laser light.
30) The best way to label CD-Rs and CD-RW’s is to use special CD marking pens whose inks do
not damage the lacquer surface of the disc. An alternate method is to use adhesive paperlabels designed for optical discs so that they do not peel off. Misaligned paper labels cannot
be pulled off a disc without damaging the surface and the reflective layer and dye below, so
be sure to use a labeling kit device for best alignment. Alignment is not as critical for audio
playback as it is for high-speed audio extractions (“ripping”) or data recordings for which
drives read at high speed. The worst way to label discs is to use a ballpoint pen.
31) The best way to store CD-Rs and CD-RWs is to keep them in cases that protect the surface
from any physical damage and the bottom from scratches. The discs should be kept awayfrom light and heat and transient debris such as dust.
32) The “speed” of a drive is its maximum speed, not its average. Claimed speeds of 32X up to
52X and beyond cannot be achieved over the entire disc because of the limitations in dye
reaction times, data transfer rates, and laser power. These maximum speeds are achieved
only if the amount of data is enough to bring the laser head to the outer half of the disc where
the disc spins the fastest--the faster the maximum claimed speed, the further from the centerof the disc. See Reference Guide.
33) “Buffer underrun” occurs when the drive asks for more data to burn on a disc at a rate fasterthan the computer can provide. The computer’s buffer memory storage can run out andinterrupt the data stream. There are several ways to avoid this problem:a. Let the computer’s RAM memory concentrate only on disc burning by making sure
you shut down all other applications, even those running “in the background” such as
anti-virus programs.
b. Defragment the hard drive so files run contiguously and the drive does not have tohunt for missing pieces.
c. Record at a slower speed.
d. Invest in a drive that has “new technology” to avoid buffer runs. (The new technology
is chiefly more buffer memory in the drive and programming that automatically slows
down the drive for you if it has to.)834) The discs are neither mislabeled nor defective. Your drive is identifying the discs as“Memorex discs” and only allowing a maximum recording speed of 24X for them because thedrive’s firmware only allowed that maximum at the time it was built. It may not recognize 48X
as a legitimate speed. You may be able to update the firmware by contacting the drive
manufacturer so that all discs rated 32X or greater will be able to achieve at least a 32X rateon your drive.
CD-RW35) CD-Rs and DVD-Rs use a dye to record data. The “burning” process of recording
permanently alters the dye. Erasable media such as CD-RW, DVD-RW, DVD-RAM, and
DVD+RW use a semi-metal alloy instead of a dye. The recording laser melts the alloy in the
spots to represent pits because melting and sudden cooling dull the alloy. The laser canerase the disc by heating the alloy at lower power because heating and cooling return thealloy to its original shiny, crystalline state. See Reference Guide.
36) The series of numbers describing drives list the maximum possible speeds the drive iscapable of reaching during: a) recording a CD-R; b) recording a CD-RW; c) reading a CDROM. A 32/12/40 drive can record a CD-R at a maximum speed of 32X; can record a CDRW at a maximum speed of 12X; and can read a CD-ROM at a maximum speed of 40X.
Note that the maximum read speed may not apply to all CD-Rs or CD-RWs. If their signal tonoise ratios are poor limit the drive’s read speed to lower values. See Reference Guide.
37) Trading in a 24X drive for a 52X drive will save you about a minute, fourteen seconds perdisc only if you record to the maximum capacity of an 80-minute disc. Recording any less will
reduce any timesavings significantly. A disc can only “explode” in a drive if it has alreadyexperienced some severe damage already that the drive makes worse. Your 24X drive isalmost as likely to explode such a disc as a 52X drive would since they both start up at
approximately the same speed. See the section in the Reference Guide on CD-R speeds fora graph of timesavings and speed ratings.
38) There are three different types of CD-RWs: a) the regular 1X-4X version; b) the “high-speed”
4X-16X version; and an “ultra-speed” 8X-24X version. Older drives with a maximum rating of
4X for CD-RW are limited to the 1X-4X discs. High-speed drives can use record both theregular and high-speed discs, but they cannot record “ultra-speed” discs even if the speed
ratings overlap between 8X and 16X. The latest ultra-speed CD-RW drive can record all
speeds of CD-RWs up to the maximum speed rating of the medium. See Reference Guide
for more details.
39) That would seem logical—if there were only two variables: good discs and bad discs.
However, the variables include the drive firmware and the packet-writing software. If the drive
firmware does not include the proper writing strategy for the CD-RWs, the drive will produce
errors on the disc that the software interprets as disc flaws. In many cases, updating thedrive firmware will solve the problem if the new drive firmware includes the discs in its
settings. Updating the packet-writing software may also solve the problem.
40) No. They will not be able to record the latest “ultra-speed” CD-RWs even though ratings may
overlap. For example, an ultra-speed 16X disc will not be able to be recorded on a highspeed CD-RW drive with a maximum speed of 16X. The 16X high-speed rating is not thesame as a 16X ultra-speed rating, or even an 12X ultra-speed rating for that matter. See theanswer above. “Ultra-speed” CD-RW drives are necessary to record onto 16X-24X ultraspeed CD-RW discs; but once the discs are recorded, all CD-RW drives are able to read
regular, high-speed, or ultra-speed discs.
41) No. A 700MB CD-RW truly has a blank capacity of 700MB, but 100MB are sacrificed toformatting so that data can be filed and erased. Double-sided high-density floppy diskettes
have an inherent capacity of 2MB, but everyone is used to the 1.44MB capacity that remains
after they have been formatted. The same applies to CD-RW.
42) It is very unlikely that a whole spindle can be defective. There are two possible reasons: 1)
your drive does not have the proper write strategy for the discs (see #39), or 2) the first disc
you tried could actually be defective but its errors corrupted temporary memory so that the9software rejects all subsequent CD-RW discs. Rebooting will take care of the second
problem, but you may have to update the drive firmware and packet-writing software to solve
the first situation.
43) “Ripping” is the digital extraction of files from a CD to a computer hard drive. As the computer
extracts the files, the software can turn them into .wav files for recording onto a CD-R as
tracks that CD players will recognize or into compressed MP3 files or into a file format of theuser’s choice. “Burning” is the word describing the laser recording process in which a highpower laser “burns” the organic dye of CD-Rs or melts the metal alloy layer in CD-RWs.
DVD and Recordable DVD44) Although the discs are the same physical size and shape, there are more tracks and smaller
pit sizes on a DVD. See Reference Guide.
45) A DVD 5 is a single-sided, single layer DVD disc holding 4.7GB of information. A DVD 9 is asingle-sided, double layer disc holding almost twice as much. There are four basic versions
with definitions in Reference Guide.
46) The storage capacity can vary depending on the number of sides used and the number oflayers on the disc. See Reference Guide for a complete listing.
47) Some newer models of DVD players follow a “multi-read” standard so that they can play mosttypes of DVDs as well as CDs, CD-Rs, and CD-RWs. Earlier versions of DVD players werelimited to DVDs, but often the circuits designed for the low reflectivity of DVDs werecompatible with the low reflectivity of CD-RWs. If those types of DVD players could readCDs, they could often read CD-RWs, too. See Reference Guide.
48) There are three different types because of a combination of different design objectives andconflicting corporate interests. Reference Guide.
49) See Figure 22 on Reference Guide.
50) This is a great argument for frightening people to abandon video tape and jump into DVD
recording, but it’s based on misinformation. As long as the chemical formulation in the binderof the video tape is sound and the tape is stored properly, there is no cause for the tape todeteriorate over time. Playing a tape over and over can reduce the signal output by 1.5 dB,
but since the signal is FM modulated, that decrease makes no difference in quality. Repeatedplaying can actually polish a tape surface so that a new recording might even test better thanthe original. (As a point of reference, modern video high quality VHS tapes are able towithstand one hour of still-frame play without deterioration. That’s equivalent to 108,000
passes or repeated plays.) Over time video tapes can suffer from:a. Edge damage from misaligned guides or poor heads
b. Wear from worn or damaged heads or transient debris getting between the heads andthe tape surface. (Debris from the edge of the tape after slitting is a major cause ofdropouts for video tape.)c. Damage caused by excessive humidity; for example, the condensation that occurs on
the tape surface if a cold tape is brought into a warm room.
d. Poor storage conditions that include heat, humidity, great fluctuations in temperature,and dust. Rewinding tapes periodically without stopping at any point in the cycle will
relieve any stresses that build up in the tape packs from variations in temperature andhumidity.
e. Exposure to strong magnetic fields
As long as good tape with sound chemistry is stored properly, it will not deteriorate. The real
truth is the reverse: the life of optical discs is defined as the point at which slow deterioration
causes the error level to reach a threshold beyond error correction. That steady deterioration
can take a very long time, but it is irreversible. A fundamental difference between the two
media is that the VCR contributes greatly to the physical quality of the tape as well as to its
playback quality. Dirty heads and guides, worn head gaps, misaligned guides, improper takeup tensions, and many other alignment issues contribute to tape damage that often appears
to be “degraded” tape. VCRs age at the same rate that tapes do, and an old, uncared-for

10

VCR may be a greater contributor to poor tape playback than the aging of the tape. DVD
players have no physical contact with the discs other than clamping the center hub.
51) A DVD-R is a recordable DVD similar in design to a CD-R. It is not erasable. Reference
Guide.
52) No, for two reasons. First, it is wrong to take the work of others without compensating themfor their efforts—and it’s illegal. The second point is that there are copy protection schemes
built into DVDs, drives, and software that prevent such illegal copying.
53) A DVD-RW is the erasable companion to the DVD-R. Use of a semi-metal alloy instead of apermanently altered dye makes the DVD-RW erasable. Reference Guide.
54) Version 1.1 DVD-RW discs have a speed rating of 1X to 2X. These discs can be recorded inalmost all stand-alone set-top recorders. DVD-RW discs with speed ratings of 4X or 6X are
known as version 1.2 DVD-RW discs. These version 1.2 media cannot be recorded in older
recorders and sometimes only play in those recorders when they are finalized.
55) A DVD-RAM is a DVD designed for random access memory, for the quick and easy storage
and retrieval of data. Its protective cartridge distinguishes this disc, but some versions comewith a bare disc free of any cartridge. Reference Guide.
56) A DVD+RW is a rewritable DVD designed to work well with both video and data recording.
The DVD+R is the write-once companion. The plus in their name distinguishes them from theearlier DVD-R/-RW. Reference Guide.
57) Whether a recorded DVD will work in a DVD player depends on the player. Multi-format DVD
players will likely play all formats except the DVD-RAM cartridges. Older players may havethe fewest problems with DVD-R or DVD+R if they play the discs at all. The lower reflectivityof DVD-RW and DVD+RW sometimes poses problems for older players. Reference Guide.
58) DVD 1X speed is already nine times faster than a CD 1X speed; so “high-speed” DVDrecording is going to be limited. All present drives can record at 1X. DVD-RAM records at a
maximum of 3X; DVD-R at a maximum of 4X; DVD-RW, 2X; and both DVD+R and DVD+RW
at a maximum of 4X. 8X writing is next increase in DVD recording speeds, and it will comefirst to DVD+R, then DVD-R, and then DVD+RW. The fastest DVD writing speed possible is
16X or just slightly faster. Reference Guide.
59) Yes, but the whole story is not quite as dramatic. The early DVD-R/-RW drives that could
write at a maximum of 2X would not recognize 4X DVD-R discs and could possibly damage
their laser diodes trying in vain to identify the discs unless the user intervened and stopped
the drive. Pioneer provides a firmware fix to the drives so that they will recognize 4X discs
and record them at 2X. See www.pioneerelectronics.com/hs/ to download the fix for theirdrives. In the DVD+R/+RW camp, 4X discs in early 2.4X drives will appear to behave
normally, but the write strategy will create irregular marks in the discs and the discs will fail. A
firmware upgrade fix for the Memorex DVD+R/+RW drive can be downloaded from theMemorex website at www.memorex.com. Memorex also provided warnings and the firmware
information in all of its 4X DVD+R and DVD-R products.
60) The problem is that computers and DVD drives and media count the numbers differently. The
computer counts according the base two in its binary system. The DVD camp decided tocount bytes in the decimal system. A 4.7GB DVD+RW actually only holds 4.377GB incomputer terms minus any capacity taken up by formatting.
a. 1GB = 1 gigabyte = 1,073,741,824 bytes = 230 in computer terms
b. 1GB = 1 gigabyte = 1,000,000,000 bytes in DVD terms
61) There are often two reasons a disc will not record in a drive: 1) the discs are the wrong
format, or 2) the drive lacks the firmware to recognize the disc. In the first case, a DVD-R
recorder will not be able to record on a DVD+R or DVD+RW disc unless the recorder is a“dual format” recorder that can record on both. The same is true of DVD+R/RW recorders—
they will not record DVD-R/-RW discs. The second case is more common, but less obvious.
Drives rushed to market with the latest speed as its chief feature often limit the testing doneon various discs in order to save development time. The drives work with a limited number ofdiscs whose ID codes are in the drive memory so that the drive selects the proper write
strategy—the amount of laser power required and the timing of the light pulses—to record on

11

them. Discs whose codes and write instructions are not in the drive memory, its firmware, will
not work or work very badly. In time the drive manufacturers develop new instructions for
additional disc ID codes, and these are added to the drive’s firmware by means of an updatethat is “flashed” to the drive’s memory bank. Internet forum groups often make ignorantclaims about discs or drives when the problems are due to incompatibilities, not any flaws ineither the discs or the drives.
62) CBR stands for “constant bit rate,” and VBR means “variable bit rate.” The CBR means thecomputer assigns the same number of bits for every second of video while VBR may alter therate depending on how complex the video is. VBR can often be more efficient and allow alittle more capacity on a disc if the video is not tough to encode.
63) VR stands for Video Recording. That’s the easy part—there are two incompatible VRformats: -VR and +VR. The –VR format is used by the DVD-R/–RW camp to record video inreal-time onto a DVD-R or DVD-RW disc in a set-top recorder so that TV programs can berecorded from the built-in TV tuner. Unfortunately, -VR formatted discs will play only on thetype of recording device that recorded video onto them. –VR recording allows playlists andchapter markers to be added to a recording on a DVD-RW and some editing ability. The +VR
mode is used by DVD+R and DVD+RW discs for the same type of real-time recording as well
as some limited editing. Unlike –VR formatted discs, +VR formatted discs will also play in
DVD players that play DVD+R and DVD+RW discs.
64) MPEG-2 encoding has a number of bit rate settings, the highest of which exceed thestandard for DVD-video. A DVD cannot have a bit rate higher than 9.8 Mbps (megabits per
second), including both audio and video. Some video capture/editing software allows higher
rates for MPEG-2, but the higher rates will not allow DVD recording, which is what mostpeople are trying to accomplish. Other software picks a lower rate by default. The “highest
quality” for some is only 6 Mbps because it is much easier to encode and more likely to workthan a higher rate. Other software limits the bit rate to 8 Mbps to offer high quality at a safer
rate than the maximum of 9.8 Mbps.
65) The “best bit rate” is the one that offers the best balance between quality and disc capacity.
Choose the highest rate possible—8 Mbps or higher—for “archival” quality, but that means
only about 1 hour per disc. Choose lower rates if getting more information on a disc is more
important than the highest video quality.
66) DVDs are capable of much better quality than that on VHS tape if: 1) the video is masteredand encoded very well, and 2) if the bit rate of encoding is sufficiently high. Capturing VHS
video at too low a bit rate will produce video far worse than that on the original tape evenwhen it is played back on a DVD player. The mastering and encoding software used by
Hollywood studios costs hundreds of thousands of dollars and is far superior to anythingoffered to consumers today. The result is that, even at the highest bit rates, video captured
from VHS tape and recorded onto DVD will not be as good as that on the original VHS tape.
The best software would only be able to make it appear equal to the original, not better. The
same holds true of MiniDV tape. It is encoded at a rate of 25 Mbps, but when that istranscoded to MPEG-2 video even at the maximum rate of 9.8 Mbps, the resulting video
quality is less than the original if one looks very closely.
67) Throwing away the masters would be a very foolish thing to do for several reasons: A) the
masters offer better quality than the DVDs made from them (see #60), and future software will
reduce that difference if you want to remake them later; B) video tapes degrade with use, notwith age (see #48) so they are safe if stored properly; C) DVDs do not degrade with use, butthey do degrade over time as the number of errors increases; and, as digital media, at somepoint they may refuse to play altogether. It is a good rule of thumb never to throw away
master copies.
68) The problem is probably that the capturing software did not accept a movie protected byMacrovision. Macrovision is an encoding method used to defeat copying of VHS tapes andeven DVDs. Capture software will often recognize tapes protected by Macrovision andprevent the video from being seen properly.

1269) The number of minutes of video a DVD recordable disc holds depends on the bit rate used tostore the video: a high bit rate provides the best quality but requires a lot of data that use up
time. A lower bit rate uses less data, but the video quality declines. The “standard practice”
appears to be similar to that for video tape: the highest quality mode (“XP” or “HQ”) allows
one hour of recording; SP (“standard play”) is 2 hours. At this point it becomes confusing: LP(“long play”) is 3 hours for some DVD+R/+RW recorders and 4 hours for others. For DVDRAM, LP provides 4 hours of recording time. Extended play EP is 4 hours in some
DVD+R/+RW recorders but 6 hours in others and in DVD-RAM recorders. Those
DVD+R/+RW recorders that designate EP as 4 hours use “EP+” for their 6-hour mode. DVDRAM recorders will record DVD-R discs in the same modes as the DVD-RAM, but Pioneer’s
DVD-R/-RW recorders offer completely different nomenclature and settings. See the chart in
the Reference Guide for the full details.
70) Recording video onto DVDs requires:a. a fast computer with a lot of RAM (>600MHz processing speed; >64MB of RAM)b. a method to capture the video so that the computer can accept the video datac. editing software to alter the program, add titles, sound tracks, etc.
d. authoring software to arrange the edited program in a DVD format with menus
e. a recording DVD drive
f. lots of time and patience Reference Guide.
71) The factors in determining which format suits your purpose depend on:a. your reason for recording at high capacity—video or datab. price of the drives and the media that support themc. compatibility with other drives or DVD players
Memorex cannot answer the question for you. Our intent is to provide enough accurate
information so that buyers can make the most educated choices.
72) Probably the one most users choose to buy, if one defines “best” as “most suited to mostusers.” Reference Guide.
73) The fastest DVD recording speed is a bit faster than 16X, a data transfer speed that canoccur only at the outer edge of the disc at the end of the recording. The speed is determinedby the fastest rate of data transferred to the disc divided by the regular data transfer speed ofvideo coming from a DVD player. There are some recorder manufacturers who are misusing
the standard terminology by comparing the time it takes to play back a full disc to the time ittakes to record it. Since it is possible to stuff as much as 6 hours or more on a hard drive in
the Extra Play EP mode by using high compression at the sacrifice of quality, transferring the
6 hours worth of video onto a DVD disc at 4X will take the same time as transferring 1 hour ofhighest quality of video; but one can claim that 6 hours at 4 times the standard 1-hour speed
is equal to “24X.” This is misleading and incorrect. The amount of data for a 1-hour highest
quality video DVD is the same as that spread over 6 hours of lowest quality video. The speed
is a matter of how long it takes to transfer data, not transfer “playback time.”74) You didn’t do anything wrong. When this happens, most people erroneously blame the discor the disc quality when, in fact the real reason is most likely an incompatibility between thedisc, the software, and/or the drive. If the drive or the software do not include theidentification code of the particular disc so that they can set the proper write strategy for thedrive (the intensity and the duration of the laser’s recording pulses), the drive can end up
making recording marks on the disc that are unintelligible for it to read later. The drive may
inform the user that the disc is illegal, corrupted, scratched, or not even in the drive. The
drive will refuse to format or erase the disc and sometimes insist that it is not a rewritabledisc. In most cases the solution is to check for firmware updates for the drive that include
additional discs and software updates for the recording software that also include more discs.
Updates may allow users to record to the remaining DVD-RW (or DVD+RW and CD-RW
discs) in a package, but the unintelligible would have to be returned to the factory to beerased by heating methods independent of drives that can no longer identify the disc.
75) There are usually two visible numbers on every disc: the production code unique to each discthat appears either as an ink-jet printed number or as a number molded into the plastic. Both13

appear around the inner ring of the disc. A second number appears in the silver alloy section
beginning around the inner ring. This number will likely appear on all the discs in a spindle
because it refers to the stamper used to mold the all the discs in a production run. The MID(Media Identification) code numbers are not visible on the disc. These numbers are in theform of digital information that is encoded into the stamper and pressed into the disc to tellrecording drives what type of disc it is, its recording speed rating, and the amount of laser
power to be used in recording the disc.
High Definition Video76) High Definition video generally means a video signal with either 720 or 1,080 horizontal linesof video information instead of the 525 lines our NTSC television standard uses. (Of the 525
NTSC lines, only about 480 actually display picture information. The rest are used forsynchronizing signals for the TV circuitry and only appear in the black bands above and below
the picture.) Some DVD players use special circuitry to repeat lines the way computer
monitors do. That means that instead of showing 30 frames of picture each second, eachframe composed of two fields interlaced together, these DVD players send a signal to highdefinition displays as both fields simultaneously composing a frame. This is referred to as“progressive scanning” instead of interlacing. Although more detail appears in a progressively
scanned DVD display, it is not true high definition. True high definition signals must have
720 lines of progressively scanned video (“720p”) or 1,080 lines of lines of information either
interlaced (“1080i”) or progressively scanned (1080p).
DVDs using their MPEG-2
compression do not have the capacity for carrying all the data needed for HDTV. There are
two ways to add high definition information to DVD discs: a) use different compression
methods to pack more information on a disc, or b) use a laser with a smaller wavelength topack more MPEG-2 data on the disc. The first method retains the standard red laser anduses new firmware in the DVD player to distinguish regular DVDs from HD DVDs. The
second method uses a blue-violet laser diode capable of much smaller wavelengths. There
are two different versions of the second, blue laser method that are capable of carrying true
HDTV video signals in the MPEG-2 compression scheme: a “Blu-ray” version and an “HDDVD” version. See Reference Guide.
77) There are several ways to see high definition programs: a) use a high definition tuner with ahigh definition monitor to receive “over-the-air” broadcasts; b) use a high definition cable box
for cable reception; c) play D-VHS cassettes that have high definition programs recorded on
special VHS tape (requires a D-VHS player, which is hard to find); d) or use one of the two
new high definition discs that are being introduced now.
78) The lasers used in CD players and drives and in CD-R/-RW burners are infrared lasers that
produce laser light at a wavelength of 780 nanometers (billionths of a meter). DVD players,
drives, and burners all use ruby-red lasers with wavelengths tuned to 650 nanometers. In
order to create DVDs capable of high definition video, engineers have had to shrink disc pit
sizes below the wavelengths of red light; so to read the pits, a new laser had to be developedwith a smaller wavelength. The laser is a blue-violet laser with a wavelength of 405 nm.
Reference Guide.
79) High definition programming requires far more data than DVD video. One way to increase thedata would be to use a different data compression scheme to pack more information on aDVD, but developers chose to use blue lasers rather than red lasers used in DVDs. Bluelasers have smaller wavelength than red lasers (Red is at the bottom of the color spectrum
and the blue lasers are closer to the upper ultra-violet—think of a rainbow!) and can read andwrite smaller data pits. Smaller data pits mean more information can be packed onto a discthe same size as a DVD. Unfortunately, the developers disagreed on how to use the blue
lasers. One group decided to use greater data compression and fit all the HD programmingon a less expensive disc much like a regular DVD. This was the HD DVD camp with its 15GB
disc. A second group decided to push existing technology to its practical limits and use
standard DVD compression on a totally new type of disc. Getting all the HD information at14

lesser compression on a single disc required more capacity; so this group—the Blu-ray
camp—designed a disc with 25GB capacity.
80) Both discs will play high definition programming equally well. In fact, unless one is watching
on a true HD screen larger than about 32 inches, high definition will be difficult to distinguishfrom standard DVD. Larger screen sizes begin to show the inter-line flaws and artifacts ofstandard video, and that is where the improvement in high definition resolution will be
noticeable. As for superiority of format, that is debatable. HD DVD discs will be lessexpensive to manufacture because they are so similar to regular DVDs, and therecorders/players can use a plastic lens to read/write discs. Blu-ray discs have greater datacapacity; and that capacity can be used with the standard DVD compression or the same
compression used for HD DVD. The choice of data compression will have a greater effect on
any difference in video quality between the two than any difference in the way the discs are
made. HD DVD’s MPEG-4 encoding can actually produce better pictures than the older
MPEG-2 compression some Blu-ray discs may use. The recording surface for Blu-ray,
however, is on the bottom of the disc and more prone to scratches and physical damage.
The disc will initially be more expensive to produce, and the recorders/players require a more
expensive glass lens to read/write discs. The “better” format will be the one more consumers
choose to adopt, and that will take time to decide.
81) In some cases it may be possible. The HD DVD Consortium has developed a special 'hybrid
disc' that contains 2 distinct sets of information: one is the high definition information that willneed a true HD DVD player to read it, and other is the standard definition information that canbe played back on today's DVD players. This is relatively easy to do since both the standard
DVD and the HD DVD use two pieces of plastic with the video data sandwiched between
them. Blu-ray discs use a single-piece design with the data on the bottom of the disc. It is
possible for such discs to have a double-layer design that includes a standard DVD program
within the disc and the high definition information in its bottom position.
82) Yes. Read heads can include multiple read lasers or multiple lenses so that infra-red laserCDs, red laser DVDs, and blue laser high definition discs can all be read by the same device.
Several leading consumer electronics companies (including Panasonic, Philips, Pioneer,
Samsung, Sharp, Sony and LG) have already demonstrated products that can read/writeCDs, DVDs and Blu-ray discs using a BD/DVD/CD compatible optical head; so you don't haveto worry about your existing DVD collection becoming obsolete. It's up to each manufacturer
to decide to make its products backwards compatible, and most see the advantage in having
players that can also read older optical disc formats.
84) No. A Blu-ray disc will not play in an HD DVD player and vice versa. However, it appears
likely that some manufacturers will manufacture 'dual format' drives, players and recordersthat could accommodate both formats in the same way that some manufacturers currently
offer multi-format DVD players and recorders that can accommodate both DVD+R/RW and
DVD-R/RW discs.

15

REFERENCE GUIDE FOR OPTICAL MEDIA
Terence O'Kelly
Memorex has long been one of the world’s foremost suppliers of media for memory storage. Thevery name of the company is a shortened form of “MEMORy EXcellence” that started in 1961 withthe manufacture of half-inch 9-track computer tape and progressed to audio and video cassettes,
digital audio cassettes, and computer diskettes. As technology developed, Memorex expanded to
optical storage media such as recordable and rewritable CDs and DVDs and has become one of theworld’s leading suppliers. Now, as the long-promised age of solid-state memory is beginning,
Memorex is also providing a wide range of flash memory devices for computers.
Today’s technology is increasingly digital. The world has quickly accepted “digital” as a distinction ofadvanced technology and quality, often without fully understanding what it means in everyday
products.
CD-Rs and CD-RWs have replaced audio cassettes and floppy disks as common
recording media, but few people know how they work. Newer optical storage products such asrecordable and rewritable DVD are designed for greater storage capacities to challenge video tapeand computer cartridges, and these media are even more complicated because of the variety ofcompeting designs and formats available. Memorex believes that many of our customers are curious
to know more about the products they are using or will be using in the near future. In ourcommitment to “memory excellence,” we hope to explain the technology behind the products we sell.
Very technical information that may be of interest only to readers with a scientific backgroundappears in the shaded passages

ANALOGUE VS. DIGITAL
Analogue comes from two Greek words loosely meaning “word for word,” as in a translation. The
adjective is a way of describing information in one understandable way analogous to or similar to theactual way. The description is often applied to the use of a “picture for picture” instead of a “word forword” translation. For example, an analogue clock has hands that make a complete circuit in aminute or in an hour or in half a day, depending on which hand it is. The hands continually goaround just as the earth turns completely around on its axis in a day. Analogue recordings “draw” animpression of sound waves in the squiggly groove in vinyl records or as variations of magnetic
energy in cassette tape. The vinyl records and tape store these “pictures” of the sound patterns andallow them to be played back. The problem with this system is that the information gets mixed up
with the flaws of the medium. A clock hand that does not keep up with the other hands gives
inaccurate information. Dust in a record groove causes sounds and noises not meant to be heard.
Tape imperfections cause hiss that was not part of the original sound.
Digital recording is a method that avoids these flaws. Digital recording does not try to draw or imitate
the information that is being saved. Instead, it converts the information into a mathematical code that
ignores the flaws of whatever medium is storing the data. To use an analogy, a canvas painting of alandscape records the landscape with all the “flaws” of canvass and paint texture (those “flaws” thatmake a painting an inaccurate but artistic impression). If oil is spilled on the painting, it is difficult torestore what was there because the oil becomes part of the record. If, however, someone recorded
the landscape with a “paint-by-number” scheme in great detail, the oil would not matter. The oil stain
had no numbers assigned to it; so the artist could reproduce the landscape by following the number

16

code exactly. The more numbers involved, the more accurate and detailed the reproduction would
be—and every copy would be almost identical to the original. 1
The word digital refers to digits or numbers. It comes from the Latin word digitus, or “finger,”because everyone learns to count on his or her fingers. We have ten fingers, so our common
numbering system is to the base 10 and uses ten digits—0 to 9. The mathematical code used indigital recordings is very intricate and needs computer chips to encode and decode; but computers
don’t have fingers. They have transistors that recognize only two states: on/off (or “0/1,” “change/nochange,” “+/-,” etc.). Computer engineers use the binary numbering system for computers, anumbering system to the base 2 that needs only two numbers, 0 and 1, to construct any value.
Expressing the same number 3723 in both our common decimal system (10) and the binary (2)numbering system shows the differences between the two.

3,723
The decimal system uses digits 0 to 9. Each column is 10X greater than the one on its right.
1 millions 100 thousands 10 thousands thousands hundreds tens ones

0

0

0

3

7

2

3

= 3,723

The binary system uses only digits 0 and 1. Each column is 2X greater than the one on its
right.
2048’s 1024’s 512’s 256’s 128’s 64’s 32’s 16’s eights fours twos ones

1

1

2,048

+ 1,024 +

1

0

1

0

512 +

0

+ 128 +

000

+ 0 + 0

1
+

8

0
+

0

1
+

2

1
+

1

= 3,723

In our familiar decimal system, each column of digits goes up by a factor of 10. The number 3723 isrepresented by 3,723 with a comma often separating each of the sections worth a thousand. In thebinary system that computers understand, 3723 is represented by the number 111010001011 forwhich each column represents a factor of 2. Each column is twice the value of the column to its right.
We count by 10’s (fingers). Computers count by 2’s (on/off transistors).
The binary digits that computers use are called “bits.” These bits are organized into “words”
containing eight bits called, in a fit of early computer geek humor, “bytes.” It is these words that
commonly describe capacities such as a kilobyte, megabyte, gigabyte, and so forth. And because
these capacities are based on a binary system, there is often confusion about the true value of thenumbers. A kilobyte literally means “1,000 bytes”; but because the number base is a 2, not a 10, theclosest binary number to 1,000 is 210 or 1,024. A kilobyte is actually 1,024 bytes in the binary way ofcounting.

STORAGE MEDIAIn the earliest days of computers kilobytes meant a lot of information. That did not last long.
Technological progress has made computers faster, smaller, and less expensive and has made thestorage media for them capable of greater capacity while also shrinking their size and cost.
Memorex’s half-inch computer tapes gave way to 8” floppy disks, then 5 ¼” diskettes, then the 3.5”
diskettes that are now being replaced by CD-Rs and CD-RWs. Figure 1 shows the enormous growthin storage capacity of modern storage media, and research continues to find ways to pack more
information in smaller media that cost less per gigabyte of storage capacity. Figure 2 is an example
1This example may be part of the reasoning some people use to explain why they believe analogue recordings to be artistically “musical”
and digital recordings to be lifeless and “mechanical.”17

of the use of that growth in capacity. Full-color pictures, audio, and video are combining with text tomake more understandable presentations than ever before. That requires more capacity.

Growth in Data Capacities
gigabytes

10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0

4.
7
-R
A
M
2.
D
6
VD
-R
A
M
D
VD
4.
7
-R
A
M
D
VD
5.
2
-R
AM
9.
4

-R

D
VD

3.
95

D
VD

2H

D
VD

-R

-R

C
D

D

Figure 1

C
D

di
sk
et
te

0.0

-R
W

1.0

Growth in Data Requirements
kilobytes

1 page ASCII text

35,00030,0001-page FAX
1-page color image

25,00020,00034,80015,0001 minute CD audio

10,0005,000

1 minute DVD video

3

50

5,000

8,780

0

Figure 2

DIGITAL AUDIOMathematicians and engineers designed computers to do calculations quickly and accurately. The
success of the personal computer (PC) and its growing sophistication transformed it from a desktop
calculator when software engineers began to write programs that would allow it to perform all thetricks it commonly does today. One of the first tricks was to record audio. Analogue audio
recordings have a fundamental problem mentioned above: they add their own inherent flaws to therecorded program. Making analogue copies of an analogue recording doubles the flaws, and thiswas a problem for early multi-track recordings (but a blessing for the music industry that feared
people making chains of copies of just one legitimately purchased record.) “Digitizing” audio, that is,18

putting it into a mathematical code, avoids that fundamental flaw. Once the audio is in a binary code,that code can be recorded as +/- pulses on magnetic tape or magnetic discs, or as microscopic
indentations on optical discs. As long as the code is accurately reproduced from copy to copy, any
minor flaws in the recording medium can be ignored. Every copy is theoretically as good as theoriginal. That assurance provided a solution for the multi-track problem (and opened up all theissues of copy protection for the music industry).
All sound is simply our ears’ response to changes in air pressure. A whack on a drum first expands
the air as the drum skin is pushed downward. Then it compresses the air as the skin bounces back.
The skin moves back and forth at a relatively slow rate (or frequency) until it finally settles down. The
low, bass sound of a drum creates changes in the air pressure at slow rates of change or low
frequencies. Hitting a metal cymbal, however, causes the cymbal to vibrate very rapidly. Those
vibrations make pressure changes in the air at a very high rate—high frequencies. Most of the sound
we hear falls somewhere in between those rates of drums or cymbals. The range of human hearing
typically runs from a rate of 20 cycles of up and down vibrations per second (called “20 Hertz”) to arate of 20,000 cycles/second or 20 kilohertz. 2
Microphones pick up the changes in sound pressure with membranes that vibrate in response to the
air hitting them. The moving membranes alter an electrical voltage signal and send it to amplifiers
that increase the signal and send it to speakers (boxes with much larger moving membranes that canmove enough air to recreate the original pressure changes that struck the microphone). The soundcan also be stored as a recording. Analogue recordings draw the vibrations in vinyl records or aschanging magnetic patterns in tape. Digital recordings take the signals and encode them before
storing them.

Digital Sound
Clipping distortion

Original analogue
signalnoise

How many values of voltage level?

# of bits ~ S/N ratio

8 bits = 28 = 256 levels of voltage
16 bits = 216 = 65,536 levels of voltage

How often are the values checked?

22k samples/sec = 11,000 Hz

Sampling rate ~ frequency response
44.1k samples/sec = 22,000 Hz

Figure 3

2

Earthquakes occur at about 8 Hz, too low to hear but easily felt. That’s why sub-woofers are “special effects” speakers in soundsystems—they are meant to create a feeling of low frequencies as much as a hearing of them. Dog whistles produce sounds beyond 20
kHz, too high a frequency for humans to hear. The human ear is most sensitive to sounds in the 3 kHz range. This happens to be therange for babies’ crying, which explains adults’ response depending on whether they are the parents or next-door neighbors.

19

DIGITAL AUDIO CODING
The encoding process takes the changing sound waves and treats them as a series of values ofchanging voltage. The wavy orange line in Figure 3 represents the changes in voltage of anelectrical signal caused by the changing sound pressure. A vinyl record would have a close
approximation of the orange line drawn in the groove; but a digital encoder would assign number
values to each point on the line based on two judgments: 1) how high or low is the signal at any
point, and 2) how often should I check it? The closer the orange line can spread to the upper limit(distortion overload) and the lower limit (the noise), the louder the signal is. The fewer the up anddown patterns it has, as in the area around the blue, the lower the frequency. The more frequent thechanges, as those around the green area, the higher the frequency. A digital encoder works bytaking millions of samples of the electrical changes and assigning values to each sample as if it were
trying to code the continuous line with a line of billions of sequential dots. The more often theencoder takes its samples, the higher the frequency it can reproduce. A mathematician by the nameof Nyquist theorized that at least two samples are needed for the highest frequency to be resolved.
Since audio engineers originally wanted to extend the sound a bit beyond the “human hearing limit of
20,000 Hz,” they chose a sampling rate of 44,100 samples/second (the blue) in order to reproduce
22,050 Hz. The green lines are examples of sampling at half that rate resolving only 11,000 Hz, andit’s obvious how much more gets missed in between the lines compared to the blue sampling. The
sampling rate determines the frequency response of the system.
The other measure is the number of the steps up and down the orange line makes. The more values
allowed (the red steps), the greater detail in defining the shape of the orange line at any one sample.
The fewer values given, the less accurate the detail will be (the purple steps). This is where thebinary coding comes to play. A system using 8-bit words will allow only 28 or 256 levels of voltage todefine the shape of the orange signal. A system using 16-bit words allows 216 or 65,536 levels of
voltage changes for far more accurate reproduction. Each bit of information provides about 6
decibels of stronger signal; so a 16-bit system theoretically provides a signal-to-noise ration of 96
decibels, far better than the 64 decibels allowed by the best high bias cassettes (74 dB with Dolby
noise reduction).
The developers of the compact disc decided on a specification for a sampling rate of 44.1 kHz and a
resolution of 16 bits to provide the theoretical reproduction of music extending to 22,050 Hz at a S/Nratio of 96 dB. Some audio engineers believe that these specifications are insufficient for the best
reproduction of music, and that is why they have introduced DVD-Audio using a sampling rate of 96
kHz and 24-bit words. The new specification means much more data has to fit on a disc, and that is
why the DVD medium was chosen instead of the CD for high definition audio.

HOW A CD WORKS
The compact disc is an amazing design of the old and the new. Its flat, round shape mimics the LP
record albums with their quick track access advantage over tape—it’s much faster and easier to findthe right spot on a disc than to spool through tape. Its digital design provides high quality sound that
does not deteriorate over time because it is read by laser light, not by any physical contact as withrecord styli or tape heads. The basic design of the players is simple even if the electronics are not.
The disc rests on a drive that spins the disc at the correct speed while a laser pickup assembly
moves to the inside of the disc to start reading the contents of the disc and identify its type.
Information mixed in with the digital audio code tells the player what addresses the laser is reading
so that the player always knows where the laser is and is supposed to go next. The tracking drive
moves the pickup assembly from the inside out as the disc is being played all the way through. The
disc drive and tracking drive are controlled by servo motors (motors that are constantly adjustingthemselves according to information fed back to them) that keep the disc at the correct speed andkeep the laser at the correct spot. The design is not much different from that of a diskette drive
except that laser light reads the information instead of a head in contact with a round magnetic sheet.

20

The real difference is in the CD. The disc is a thin piece of optical grade polycarbonate with billionsof pits molded into it in a continuous outward spiral. The arrangement of the pits is the digital codefor the audio signal as well as all the information to tell the player where to move the laser pickup.
The laser shines its light up through the bottom of the disc onto the pitted spiral and follows it. The
light is reflected back by a shiny layer of aluminum deposited on the disc during manufacturing. A
thin coat of plastic resin protects the aluminum from oxidation and damage, and a silk-screened
coated label covers the resin. The top surface of the CD is more susceptible to damage than thebottom. The bottom is solid plastic, and the laser actually sees the bottom of the pits as “bumps”

spindle motor
laser lens

tracking sledmechanism

laser pick up
assembly

Figure 4rather than pits. The laser focuses on the aluminum layer above the surface of the disc’s bottom sothat mild scratches or smudges on the bottom are not seen. The plastic helps in the focusing byacting as a lens and reducing the width of the laser from 0.8 millimeters as it enters the clear plastic
to 0.001 millimeters at the aluminum layer. The laser light focused on the inner aluminum layer isreflected back to an optical sensor in the CD drive, and the sensor’s electronics interpret the change
in the angle of reflection as the laser moves over the bumps (pits) and flat areas (lands) as a“change/no change” binary digital code containing the audio and address information the drive
needs. The designers knew that there was a great possibility of errors in the system due tomanufacturing imperfections and slight damage from handling; so the information on the disc is
scrambled and spread to different places so that a scratch, for example, does not wipe out an audible
part of the sound. The electronics in the player find and reassemble the information and fix whatmight be missing or incorrect. Then the electronics send the corrected signal on to an amplifier.

21

The CD was designed with audio recording in mind, and the specifications for audio recording are
published in the “Red Book” standards. 3 In 1984 Philips and Sony introduced the Yellow Book
standards for using compact discs as data media. The difference is significant and explains why
software for recording audio on CD-Rs is so different from recording data. All CDs, CD-Rs, and CDRWs have errors. An audio error is often imperceptible to a listener; but a single data error canchange the value of the information or even crash a system. Extra efforts go into identifying andcorrecting data errors for just that reason.
Audio information is divided into frames of 24 bytes of digital audio in the form of twelve 16-bit
samples, and 98 of these frames fit into one block (24 bytes x 98 frames = 2,352 bytes per block or
12 samples x 98 frames=1,176 samples per block). A block in audio terminology is the same as asector in data terminology. The blocks are only 1/75 of a second long in time intervals; so in one
second the CD player sees 1,176 samples per block x75 blocks per second=88,200 samples, half ofwhich are devoted to one of the two stereo channels. Half of 88,200 is the 44.1k sampling rate foraudio. Red Book specifications also include two methods of error detection and the correction of
those errors, a system known as the Cross Interleave Reed-Solomon Code (CIRC). The first methodof detection adds extra information to the audio data in the form of parity bits. Almost 25% of thetotal capacity of an audio disc is repeated information to account for errors: for every 24 bytes ofaudio data, another 8 bytes of parity information are added. The second method is interleaving, thatis, spreading the bytes from one block to many others so that a major defect in one spot on a discdoes not wipe out a whole block or more. The 24 bytes of one data block will end up appearing in
109 other data blocks as part of the encoding. Cross interleaving makes sure the distribution of data
occurs over both short and long time intervals as a further precaution. Minor damage to a disc will
end up affecting small bits of many blocks instead of wiping out blocks altogether.
A CD player’s decoding system has two stages of correcting errors it finds: after audio data arereassembled in the proper order by deinterleaving (and block reconstruction using the redundantparity data, if necessary), the C1 stage corrects one or two small errors in a frame, errors such as
noise in the signal. If there are three or more errors, C1 marks the whole frame as suspect andpasses it back to be deinterleaved again before going on to the C2 stage. The C2 stage corrects up
to 2 larger errors caused by damage to the disc or debris; but if there are 3 or more errors, the data
are deinterleaved once again and passed on to the CIRC at the sector level. Test data defining
errors will refer to E11 and E21 errors. That means “Errors: 1 bad byte corrected at the C1 stage” or“Errors: 2 bad bytes corrected at the C1 stage.” The C1 stage cannot correct E31 errors or more; so
the C2 stage is called into play after deinterleaving that redistributes the group of bad bytes into their
original blocks. The C2 stage should then find fewer bad bytes to correct. E12 and E22 errors arethose that the C2 stage can correct. An E32 error is uncorrectable.
An uncorrectable audio error can still be tolerated because the error correction circuitry can “guess
what the byte should have been through interpolation algorithms or, as a last resort, quickly mute theoutput or cause a click. Uncorrectable data errors, however, are completely intolerable. No one
wants a computer “guessing” what the payroll should have been or “muting” an employee because it
couldn’t read a Social Security number. CD-ROMs (that is, CDs, CD-Rs, or CD-RWs with data
recorded on them) have all the audio error correction systems plus another system called Layered
Error Detection Code and Error Correction Code that has additional parity information recorded andeven more scrambling of data. The difference is apparent in the layout of the block/sectors of
information for Red Book audio and Yellow Book data recording. It is also apparent in the fact thatan 80-minute CD-R disc filled to capacity with audio programming holds 807 megabytes of
information while the same kind of CD-R that is filled to the same capacity in a data format will hold
only 702 megabytes. The difference between the two measurements of capacity is the extra error
correction required for the data disc.
3*The colors of the books represents their subject matter: Red = digital audio; yellow = CD-ROM; blue = enhanced music CD; white =video CD; orange = CD-R and CD-RW

22

2,352 bytes
2,352 bytes of audio

CD audio “block”:

CD–ROM “sector”: 12
synchronization

4

header data

2,048 bytes of user data

4

8

EDC blanks

276

ECC

The addition of 12 bytes of synchronization data, 4 bytes of header information, and 288 bytes ofadditional error detection and correction on top of the CIRC protection that audio discs use increases
the ability to correct errors. If a CD-ROM drive does find an uncorrectable error, it will make a certain
number of retries to correct it. This process will slow down the data rate until the drive is able tocorrect the error or until it gives up and rejects the disc as defective.
BLER is a commonly used term describing Block Error Rate, the number of blocks or sectors per
second that have bad bytes. The Red Book specification allows a BLER of up to 220 per second
averaged over 10 seconds as the maximum allowable rate. Molded CDs fall well below that figure,and good, new CD-Rs are often even better than molded CDs in terms of errors. BLER is often
offered as the “best figure” to determine good CD-Rs, but there are over fifty other important
specifications that define true CD-R quality. BLER is only one of many quality characteristics.
(Comparing BLER rates can be as misleading as rejecting a dinged up used car for “having had too
many accidents” in favor of a car with just one mishap—one that put the engine in the back seat!)

Figure 5
The bumps and lands on the CD do not represent the digital 1’s or 0’s. It’s actually the change
between them, the edges, that are the 1’s. The change in the angle of laser light reflection caused
when the light changes depth is what makes a binary 1 in the CD code. Therein lies a big problem,
though. It’s impossible to have two edges next to each other, so how can two 1’s follow each other ina binary number if there can’t be two edges next to each other? Engineers got around this problem
by coming up with another coding system called EFM, which stands for “Eight to Fourteen

23

Modulation.” This system makes sure that there are at least two binary 0’s between any binary 1’s
so that the bumps or lands do not get too small. It also limits the number of 0’s to no more than 10
between any two 1’s. 4
Figure 6 shows the RF (radio frequency) signal that the optical sensor creates from the reflected lightchanging between the bumps and the land. Below the graph you can see the edges of the pits
where the digital “ones” appear. The flow bit information coming from the RF signal undergoes evenmore decoding because there are error correction codes built into the system. The designers of the
CD system expected errors due to scratches or dust on the CD; so they included two ways toovercome them: 1) a check code to figure out where an error might be and what the real number is
supposed to be (the “Reed-Solomon code”), and 2) spreading out the information instead of keeping
it sequential. The second method, called “interleaving,” means that if there is a flaw on a disc, theflaw will not cause damage to all the music around it because the music information is spread out indifferent places. A wrinkle in cassette tape is very audible because the music around the wrinkle
cannot be picked up. A scratch on a CD, however, may not be audible because the data under thescratch is from different bits of music. The CD player reassembles the scattered data in the rightorder and corrects what it believes to be errors in the code. CD players are actually a bit like minicomputers designed to interpret, sort out, and correct all of these codes.

RF Signal Generated from the “Pits”
Pit track

10000000000100000010000000000010000000100000000010000100010000100001

The radio frequency signal is decoded into analog sound.

Figure 6

The entire system was designed to provide the best quality sound at the time it was being developed,with no physical wear to the disc and a tremendous amount of computer coding to find, fix, or hideerrors. As amazed as people were when CD’s first arrived and worked well, the second question
after “How do they work?” was “When can we record on them?” That process took a longer time andinvolved the work of chemists in addition to mathematicians, engineers, and programmers. Together
they developed the CD-R.

4

This means the bumps and lands come in discrete lengths of as little as 3 bits (referred to as 3T for a 1 and two 0’s) andno more than 11 bits (11T for a 1 and ten 0’s). 3T is the smallest a pit or land can be; 11T is the longest. Test data for CDRs often refer to signal strength at 3T and 11T to define how accurately the media reproduce the proper signal fromsmallest bump or land to the longest bump or land.

24

CD-RS
The recordable CD has a structure similar to that of the CD in that it is a molded piece of opticalgrade polycarbonate plastic with a reflective layer and a plastic resin protective layer. The
differences are that instead of a spiral of pits molded into the plastic, the spiral is a groove that isnearly 3.5 miles long. This groove has a wobble in it in the form of a sine wave at the precise
frequency of 22.05 kHz (half that of the 44.1 kHz sampling rate for audio CDs). The wobble is there
as a way to tell a CD-R recording drive to write at the proper speed and to follow the groove
precisely. Unlike a CD, the reflective layer is not deposited directly on the plastic. There is a layer ofphoto-sensitive organic dye that lies between the plastic and the reflective layer and fills the groove.
The reflective layer lies on top of the dye (Fig. 7). The dye would corrode aluminum, so the reflective
layer is silver or a silver alloy. In some cases gold is used instead of silver.

CD-R Writing
Organic dye

Figure 7

5.5 to 6.5 mW of burning power at 1X
CD players use only .5 mW of power.

The protective plastic resin is coated on top of the reflective layer just as in CDs. The recording
process works by using a laser with at least 10 times the power of a reading laser to “burn” the dye ina pattern resembling the 3T to 11T bumps and lands of a CD. The burning laser changes the dye sothat light can no longer pass easily through these spots, and during the playback process the light of
the reading laser is deflected as it crosses a burn mark in a way very similar to the deflection in a CD
when the light crosses the edge of a bump. The pattern burned into the groove of the CD-R works
for the playback laser just as the pattern of bumps and lands works on a CD.

CD-R DYES
There are several different types of dyes and reflective layers used in CD-Rs. The first type of dye
was a cyanine dye 5 that has a greenish color when visible light is reflected back from the silver or

5“Cyanine” because the dye is blue. It has nothing to do with the poison cyanide.

25

gold mirror layer. A second dye called phthalocyanine 6 later came onto the market with different
characteristics. Although it would appear as yellow against a gold layer or as slightly green/yellow oreven clear against a silver layer, it, too, is a slightly blue color. This dye needs slightly less laser
burning power during recording; and its burn marks leave a tiny depression in the layer that hashelped give this dye a reputation for excellent stability in heat and light, two of the dangers topreserving CD-R integrity. A third dye is azo-cyanine, which has a bright blue color on CD-Rs. Thisis a less common dye for CD-Rs than the first two.
Cyanine dyes react to laser power more slowly than phthalocyanine dyes. The laser power isapplied in what is called a “long write strategy” to make the proper pulsed burns on a CD-R. For thisreason cyanine dyes work well at slow writing speeds. The phthalocyanine requires a “short write
strategy” that does not work as well at the slowest speeds but does perform very well at the faster
speeds. Because there is a difference in the way the dyes react to laser power and there is also a
difference in recording speeds drives are capable of achieving, CD-Rs have information molded intoa pre-groove section to assist the drive in determining the best settings. This section is known as the
ATIP (Absolute Time In Pre-groove) section. Absolute time is the time counted from the very
beginning of the disc to the end. Additional information tells the writing drive whether the disc is a
CD-R or a rewritable CD-RW, the type of the dye used and the recommended power setting for thelaser to start its testing, the spiral length in blocks (which means whether the disc is 63, 74, or 80
minutes long), the maximum rated speed for recording (up to 8X), and whether or not the disc is aregular CD-R or a digital audio CD-R (“music CD-R”) that can only be recorded in drives whosepurchase price includes a fee for copying. Although the disc has a recommended power setting, thedrive will do its own optical power calibration (“OPC”) on a reserved area of the disc to determine thebest power level. This reserved section falls within the lead-in area of a disc, an area that CD-ROM

CD-R Dyes
Cyanine•••••Figure 8“green”
Needs 6.5mw of laser
recording power
Altered region on CD-R
is not much bigger thanarea illuminated by thelaser beamLong write strategy
Excellent at slow writing
speeds

Azo-cyanine
•
•
•

•
•
•
•

• “bright blue”“yellow” or clear
Needs 5.5 mw of laser• Less common thanrecording powerother two dyes
Altered region on CD-R is
physically depressed bylaser; beam affects a• The standard dye forlarger area than that
DVD-R
illuminated by the beam
Short write strategy
Generally greater light andheat resistant than cyanineMore expensive
Excellent at high writing
speeds; poor at 1X

drives and audio players do not read. There are 100 testing partitions for OPC tests so that the disccan be reinserted and retested no more than 99 times after its first test, as long as the disc is not
finalized after recording. The drive starts at the recommended power and then tests at seven levels
below and seven levels above that recommendation. It then checks the output of the test to see
what level worked the best. Some drives will then stick to that level while more sophisticated drives
may perform a “running OPC” to continually monitor output and adjust power accordingly. These test
6

The ph/th is a strange combination of the Greek consonants ϕ and θ that should only appear together when the first is at the end of one
syllable and the other at the beginning of the next sylllable, as in naphtha, the Greek word for “rock oil” (as in naphthalene and Fels
Naphtha soap). Sir Patrick Linstead discovered a new class of organic dyes in 1933 and coined them phthalocyanine dyes from the words“naphtha” and “cyanine.” He was a chemist, not a linguist.

26

steps are important because the laser’s output can change as it ages, and the discs may have slightdifferences from the inner part of the disc to the outer edge. Once the testing is done, the drive isready to record. The laser starts from the inside and works its way to the outside of the disc. Record
players worked the opposite way, and that caused problems with vinyl discs of different diameters.
The inside-out method allows recorders and players to handle discs of different sizes and dimensions
without resorting to special adapters.
The official specifications for CDs are written in a book known as the “Red Book.” The equivalent for
CD-Rs and CD-RWs is known as the “Orange Book,” first released in 1990. The Orange Book
describes the various sections of a CD-R disc assigned for particular tasks. They are, in order:
1) The Information areaa) The pre-groove area (most of which is accessible only by recorders)
1) speed control information
2) ATIP code—Absolute Time in Pre-groove mentioned above
3) MID code—Manufacturer’s IDentification code to assist the drive firmware inselecting the proper laser power and pulse rate. The code also identifies thetype of disc4) PCA—Power Calibration Area, a test area for determining laser writing power.
This area is suitable only for speeds up to 16X. The drive may calculate
the power needed for higher speeds, but the Orange Book also added aa second PCA in the lead-out area to conduct true high speed power testingin a section of the disc that allows more physical room at the outer edge ofthe disc.
5) PMA—Program Memory Area that holds track information for all sessions
recorded to the disc before the final table of contents is written.
6) Lead-In Area reserved for the final table of contents.
7) Program Area holding all the data or music recorded on the disc. This is thelargest area of the disc.
8) Lead-Out Area that tells playback devices that the end of the disc is near.
There are two terms used to describe the completion of a recording session: “fixation” and“finalization.” Fixating a disc means writing the table of contents (TOC) in the lead-in area andwriting the lead-out areas on the CD-R disc so that the disc can be read in drives and players. CDROM drives and audio players look for the TOC when a disc is inserted; if it is not there, they cannot
recognize the disc. If a disc is not fixated, the only drive that can handle the disc is the recording
drive. That drive relies on another reserved area of the disc that lies just after the OPC area and iscalled the Program Memory Area or PMA. Recordings made at different times or in increments suchas track-at-once or multi-session recordings store temporary TOC information in the PMA section inorder to allow additional recordings to continue until the disc is full and has to be finalized. Finalizing
a disc writes the final TOC and closes the disc so that no other recordings can be made to it.
Recording in the disc-at-once mode writes the lead-in with its TOC, the pre-gap, all the disc’s tracks,
the post-gap, and the lead-out areas in one non-stop session. It is the safer way to record CD-Rs
because the recording laser operates continually and leaves no breaks in the recording that could
contribute to errors. Recording in the track-at-once mode forces the laser to stop and start after
each track, and the stopping and starting increase the possibility of errors. Multi-session recording
also runs the risk of gaps between sessions causing errors, but modern drives seldom run into these
problems today.

CD-R REFLECTIVE SURFACES
The original reflective surface for CD-Rs was gold. Gold has the advantage of being immune tooxidation. It does not tarnish or rust. The disadvantage of gold, however, is its cost. Attempts to thinout the gold layer too much can cause some audio problems if the reflectivity varies enough to cause
the signal output to waver and interfere with the servo motors in the drive. Thick gold layers do not27have this problem, and the silver alloys are inexpensive enough that there is less need to thin themout. Gold mirror layers are also less reflective than silver alloy layers and in some cases that can
reduce the top recording speed unless steps are taken to improve light transmission through the dye.
Since slower speeds often improve recording quality, and gold discs are intended for the optimumarchival quality, slower speeds work to their advantage in promoting longer life. Figure 9 lists theadvantages and disadvantages of the different types of reflective layers used for optical discs.

Figure 9
CD-R CAPACITIESCost was also a factor in the design of the CD system. Exacting precision is very expensive, so thedesigners decided to keep the expense in the mastering equipment that made the impressions (pitsor wobbled groove) in the discs. Relatively inexpensive drives just have to follow the precise guides
rather than duplicate them themselves. The guides for the CD-R start in the pre-groove area with the
ATIP information. One of the important bits of that information is the capacity of the disc. The
original CD-Rs held 63 minutes of audio or 550 MB, and 74-minute/650 MB discs soon followed. 80minute/700 MB discs are now the most popular capacity for home recording. Greater capacity intape means longer lengths unless the tape speed is reduced. In CD-Rs, however, the size of thedisc does not change to hold more information. What changes is the speed of the drive, the distance
between the grooves (track pitch) and the size of the burn marks. 80-minute CD-Rs spin more slowly
than 74-minute discs to increase capacity in a manner similar to T-120 video cassettes offering 120
minutes at standard play and 360 minutes at extended play
Figure 10 lists the different speeds of the different capacity discs, and one can see how the larger
capacity discs slow down to fit more information on the disc. When the disc slows down, the burnmark sizes have to get smaller to fit more information onto the disc. The older 63-minute discs had acomfortable margin to work within, and there were fewer problems with those discs in various drives
than with discs of larger capacity. Old CD players may sometimes have trouble playing 80-minutecapacity discs; and Figure 10 shows why: the minimum spacing between the burn marks is almost
the same as the wavelength of the laser light before the polycarbonate acts as a lens to focus thebeam on the mirror layer. Customers are often quick to blame a disc for poor quality when the
problem may actually lie in a drive’s inflexibility to “go beyond the limits” for which it was originallydesigned. Computer drives generally have the most flexibility in handling higher capacity discs.

28

Older car and portable CD players and even some of the most expensive audiophile players areoften the least flexible.

CD-R Capacities• Recording area on 63-, 74-, and 80-minute discs is identical– 22.05 kHz wobble has a range of peak-to-peak spacing at 2% of spacing
between tracks• 63.5 microns for 63-minute discs• 54.4 microns for 74-minute discs• 50.3 microns for 80-minute discs

Direction of the track– Spindle motor locks onto wobble for precise linear velocity• 1.4 meters/second at 1X for 63-minute discs• 1.2 meters/second at 1X 74-minute discs• 1.1 meters/second at 1X for 80-minute discs– Minimum spacings for optical data marks• .97 microns for 63 –minute discs• .83 microns for 74-minute discs• .77 microns for 80-minute discs (the laser wavelength is .78 microns.)

Figure 10
The red sine wave wobble in Figure 10 is not to scale. It is exaggerated to show what the “peak-topeak” spacing is (the distance of the black arrow touching the orange lines). The built-in wobble tone
guides the laser pick up drive in the recorder to follow the groove in the CD-R and tells the spindle
drive to adjust its speed to keep the tone at 22.05 kHz for 1X speed or an exact multiple for higher
speeds. Once the marks are burned in, they become the guides for a CD playback drive.

CD-R SPEEDS
Recording a CD-R in real time is just like recording an audio or video cassette—the recording
process takes just as long as the playback. A 74-minute CD would take 74 minutes to record,
frustratingly slow when a computer could process information far faster. Improvements in CD-R
manufacturing and CD-R drive capabilities soon sped the recording process to 2X, then 4X, 8X, 16X,
and now to 52X. The first speed increases were widely welcomed, but the latest changes have led toquestions about the real benefits of faster recording times. The timesavings are most meaningful if
the discs are filled to capacity because the rated speed is really only the maximum speed at which
the laser records at the outer half of the disc as it fills up. Recording speed refers to the rate that thelaser records, not to the rotational speed of the disc. See Figure 11. The fastest drives will start atjust below 24X recording speeds (with the disc spinning about 10,600 rpm) at the hub area of thedisc because that is the fastest rotational speed the disc can handle before encountering the physicallimits of balance and wobble. As the laser moves away from the hub area toward the center on its
way to the outer edge, its laser recording speed increases and the rotational speed of the discdecreases. Most users do not fill their discs to maximum capacity; so they may not allow the fastest
drives to reach their fastest recording speeds. Replacing a 24X drive for a more expensive 32X drive
will reduce the record time on a full 80-minute disc by fewer than 90 seconds per disc—if thecomputer can keep the data flowing at a speed that can keep up. If the drive is faster than the data
flow, one of two things happens: 1) the data buffer that stores the information before sending it to thelaser control runs out of room (a “buffer underrun” that ruins the recording), or 2) the drive slows

29

down under the recommendation of software that prevents buffer underruns. The latest 40X, 48X,
and 52X drives are more expensive because, like 16X drives, they operate at tremendous initialrotational speeds that can damage bearings of lesser drives if discs are even slightly out of balance,
and they often incorporate software that slows them down if the computer cannot supply data fastenough. Most of the latest drives also incorporate greater buffer memory to reduce the problems ofunderruns; but unless the host computer is fairly fast, a user may find his or her expensive “super”
drive smart enough to slow down to the same speed as that offered by the 12X or 16X drive it
replaced.

Increasing laser
recording speed

Steady discrotating speed

Figure 11

Business
card

Pocket CD-R

52X CD-R Recording Drive
Maximum Recording Speed: 52.14X
Starting Speed:
22.82X
Average Speed:
39.38XThe original design for CDs had the laser pick-up seeing the pits travel above it at a constant rate or“constant linear velocity.” That means that the disc turns at a defined rate at the beginning (about
500rpm) when the laser is reading the area closest to the hub and slows down to about 200rpm as
the laser moves to the outside edge so that the music data are being transferred at a steady 150
kilobytes per second. That worked perfectly for audio CDs because there was no need to go fasterthan the tempo at which the music was supposed to play. When CD-ROMs with data information
appeared, there was an advantage to speeding them up in order to transfer data faster to thecomputer or to the game console. A higher fixed speed or “constant angular velocity” became thenorm for CD-ROMs. In the race to produce ever-faster CD-R drives as a way to develop market
differentiation, manufacturers have developed two variants of both of these methods for high-speedrecording. In order to relieve drives of the stress of high rotational velocities, the “super” drives canwork their way up to their highest rated speed in two different ways: 1) Zone Constant Linear Velocity(Z-CLV) and 2) Partial Constant Angular Velocity (P-CAV). See Figure 12. The result has been ageneral misunderstanding of the speed ratings of CD-R drives.
A 12X/4X/32X designation describes a drive that records CD-Rs at a maximum speed of 12X;
records a CD-RW at a maximum speed of 4X; and plays back a CD-ROM or extracts audio from anaudio CD at a maximum of 32X. A high-speed drive labeled as 24X/10X/40X can record a CD-R at
a maximum speed of 24X, but Figure 11 shows why ”24X” does not take half the time as “12X.” The30

drives have to build up to the maximum speed; and if the disc is not even half full, the burner may
never reach its maximum rating. The 80mm Pocket CD-Rs and 61mm CD-R business cards will
never allow a “super” drive to reach its maximum speed. Another point worth noting is that the “40X”
CD-ROM rating applies to well recorded discs. Discs with lower signal-to-noise ratios or errors will
prevent the drive from reading at its maximum rating. Buyers who expect to cut their recording timein half by upgrading from 12X CD-R burners to 24X burners may be surprised at how little time isactually saved. Figure 13 shows a chart with the actual maximum time savings one can expect
upgrading from one speed to another; below the graph is a chart of the actual average speed of a
52X drive at different speeds and the maximum time saved

Four Writing Speeds Compared
CLV

Constant Linear Velocity

speed
time

Z-CLV

Zoned Linear Velocity

CAV

Constant Angular Velocity

P-CAV Partial Constant Angular Velocity

Figure 12

maximum
recording
speed
4X
8X
12X
16X
24X
32X
40X
48X
52X

total time to record aaveragefull 80-minute disc effective speed
21:12
10:42
7:14
5:30
3:55
3:20
3:10
2:46
2:39

3.8X
7.5X
11.1X
14.5X
20.4X
24X
25.3X
28.9X
30.2X

maximum timesavings for next
higher speed
10:30
3:28
1:44
1:35
:35
:10
:24
:05

Figure 13
The misunderstanding of the difference between the laser writing speed and the actual drive
rotational speed has promoted unnecessary concern about the integrity of CD-Rs within high-speed
drives. Stories of discs “exploding” because of the high rotational forces within drives have reachedthe level of urban myth. Discs with damaged center hubs or badly eccentric shapes can, if
improperly clamped within a drive, fracture and actually break apart. Such a situation would be dueto the original disc damage increasing enough under stress to become more apparent. These“problems” existed with high-speed CD-ROM drives and even with drives rated below today’s highest

31speed ratings. Figure 15 is a graph of the rotational speeds of a 52X high-speed drive (yellow line)
and a 20X drive (red line). Both begin to spin the discs at speeds equivalent to approximately 20X
although their actual rotational speeds may be 10,600 RPM versus 9,600 RPM.

Comparison of CD-R Speeds

minutessaved

actual average speed

35

25

30

20

25
20

15

15

10

10
5

5
0

0

4X

8X

12X

16X

24X

32X

40X

48X

52X

Figure 14

Figure 15
There is little actual rotational difference between the two, but a damaged disc that does not fracture
at 9,600 RPM may not be able to keep itself together at an additional 1,000 RPM. The fault lies inthe disc damage, not in “excessive” drive speeds. A badly damaged disc could also fly apart in a
20X drive. The limit of high-speed CD-R recording appears to be 52X for several reasons:

32
52X

1.
2.
3.
4.

There are no appreciable time savings. 52X is at best only 5 seconds faster than 48X.
The flatness of a 56X would have to be perfect.
The mechanical problem lies in any wobble at the outer edge of a disc or in any eccentricity.
The cost of a 56X disc would be greater than a 52X.

These four reasons are why 52X CD-R recording speed is the limit, not a fear that discs will be
exploding in users’ drives.

CD-RW
The marks burned into a CD-R dye layer are permanent. They can’t be changed. For users
accustomed to recording over magnetic tape and magnetic floppy discs, this can be a real handicap.
Researchers looked for ways to make a disc that could be erased, and they came up with the CDRW. Instead of an organic dye layer, this disc has layers of a semi-metal alloy vacuum deposited in
between two dielectric layers that act as insulation to trap the laser’s heat and to prevent it fromdamaging the disc. The alloy has two states: a glass crystal state and an amorphous (Greek again,
for “formless”) state that does not allow laser light to pass through. Heating the alloy to 200° C. (320°F.) with laser power causes it to crystallize so that it allows some light to pass through to the reflective
mirror layer composed of a combination of titanium and aluminum (the dielectric layers contain sulfurthat would tarnish silver.) Not much light bounces back, only 15 to 25%; so the drive needs anautomatic gain circuit to boost the light reading. (DVD players have the same circuit built into them.
That’s why some DVD players can read CD-RWs but not CD-Rs.) Raising the laser power to 600° C.
(1,112° F.), however, melts the alloy so that when it suddenly cools afterward (“quenching”) the
melted spot becomes dull and allows almost no light to pass through at all. This method of altering
the light transmission of the disc one way or another is called “phase change” recording and is themethod used not only for CD-RW but also all the versions of recordable DVDs. The entire disc canbe erased by recording over it with the lower laser power to heat the alloy enough to turn it into its
glassy crystalline state again. The fact that lower power “erases” the disc is a big advantage inphase change recording systems because the lower power can erase before higher power writes,
and that allows direct overwriting of the medium without having to erase an entire disc prior torecording on it. The light reflection process is similar to that of CD-Rs with two exceptions: 1) CDRWs, like floppy discs, need a file structure formatted on them, and that takes up to 23% of the disc’s
capacity; and 2) after time the alloy’s ability to change its form has decreased enough that
uncorrectable errors prevent its further use. The general rule is 1,000 erase cycles are the safe limit
for CD-RW discs. The manufacturing process for CD-RWs is much trickier than that for CD-Rs
because of the metal deposition processes (called “sputtering”); so it is unlikely that the two media
will ever cost the same.
CD-RW discs have a reputation for being unstable that is undeserved. Phase change alloys areaffected by extreme heat in order to change their physical state whereas CD-R dyes are affectedboth by lesser amounts of heat and ordinary sunlight. Chemical changes in the phase change layers
due to ion migration or oxidation are potential problems for CD-RWs if they have not been
manufactured properly. Both CD-Rs and CD-RWs use optical grade polycarbonate as a basematerial, and this type of plastic absorbs water. High levels of humidity can be a factor in reducing
the storage life of optical discs if the humidity reacts with the mirror layers on the discs or thechemical stability of the phase change alloys. CD-Rs that use gold as a reflective layer are superior
in this regard because gold does not oxidize. The reputation for instability may come from otherfactors such as packet-writing software problems. The original design for CD-RWs was to provide anerasable CD-R. However, the temptation to make them “optical super floppy diskettes” required aformat structure written on the discs with error correction and sector addressing built in. Data would

33

be written in “packets” with a mechanism to link blocks so that files could be altered or deleted
without interfering with existing files. Unfortunately, software companies came up with mutually
incompatible format systems. The “instability” of CD-RWs is very often due to conflicts ordeficiencies in packet-writing format systems, not to the disc itself. Filling a CD-RW to its capacity,
for example, can stifle error correction sorting of files enough that adding files causes the disc to be
unreadable. It is best to leave some extra space on all rewritable media to allow room for the error
correction processes to work effectively.
CD-RWs have not avoided the pressure to develop faster recording speeds. Unfortunately, there aresome significant differences in the way the phase change material in CD-RWs works and the way
photo-sensitive dyes in CD-Rs work. Photosensitive dyes work over a wide range of recording
speeds, but the semi-metal alloys in rewritable CD-RWs have a much narrower range of compatibility
for recording speeds. The original design of CD-RWs limited the fastest recording to 4X, 4 times
audio playback speed. In an attempt to increase CD-RW writing speeds to keep up with the trend inincreasing CD-R speeds, engineers changed both the formatting process so that some formatting
was done during recording and also changed the design of the disk and recording drives toovercome earlier restrictions that limited CD-RW recording speeds. The design changes mean thatolder 1X-4X drives are not able to record the faster 4X-16X “high-speed” CD-RWs. Even though theolder CD-RWs rated at 1X-4X and high-speed CD-RWs rated at 4X-16X share a 4X speed, it is not
the “same 4X” speed. The two versions share only the speed rating; but the “write strategy,” that is,
the amount of laser power and the timing of the light pulses, is different. Only high-speed CD-RW
drives can record high-speed CD-RWs. Because older 1-4X CD-RW drives do not have the proper
write strategy to record high-speed CD-RWs, engineers have prevented their ability to write at all on
these discs by shifting the Power Calibration Area in the ATIP on high-speed CD-RW discs. Whenan older drive looks for and cannot find the PCA where it expects it to be, the drive gives up andsends an “invalid” message to the user. There is nothing wrong with either the drive or the medium.
They are just not designed for each other. High-speed drives do recognize and are able to use theolder 1X-4X CD-RW discs at their maximum 4X speed.
Unfortunately, 4X-16X was not enough. In order to move to even greater CD-RW speeds, a new
speed rating of “ultra-speed” has been introduced with a range of 16-32X. Once again there is aproblem with overlapping but incompatible speeds: high-speed CD-RW drives cannot record onto
ultra-speed CD-RW discs even if the speed range overlaps at 16X. Ultra-speed CD-RW drives canrecord any disc; but high-speed drives cannot write to ultra-speed discs no matter what the speed
rating is. This is a cause of great confusion, and the small logos identifying the discs do not do muchto clarify the limitations.

CD-RW Rewritable Discs••

Quaternary crystalline metal alloy instead of dyeo Sputtered layers of indium-silver-antimony-telluriumo Crystallizes at 200° C. under 4-8 milliwatts of laser power Crystalline state allows a reflection of 15-20% of the laser light during read
operationo At 600° C. (8-14 milliwatts of power, 1X speed) the alloy melts to amorphous state Sudden cooling leaves the alloy dull, with little light reflected backo Two zinc-sulfide and silicon dioxide dielectric layers blanket the alloy to trap heat
Alloy’s behavior deteriorates beyond 1,000 erasures; leaves uncorrectable errors

In order to offer some guidance for CD-RW users, there are three logos to distinguish the different
speed ratings of CD-RW discs with barely discernable lettering on the side of the original logo. See
Figure 16 below. Once any of the CD-RW discs is recorded, it can be read in all CD-RW drives that
use the same packet-writing software. Reading data is not the problem. Only writing the right disc in
the right drive is a concern.

34

INCOMPATIBLE SPEED RANGES OF CD-RW DISCS

1x

4x
ORIGINAL

8x

12x

HIGH-SPEED

16x

20x

24x

ULTRA-SPEED

32x
ULTRA-SPEED+

Figure 16

MINI-DISCSony introduced the Mini-Disc format as a recordable optical disc well before CD-Rs were available.
The Mini-Disc is in the class of magneto-optical discs, discs that work on very different principles
from those used in the CD-R and CD-RW discs. The Mini-Disc was a real break-through in recording
technology, but its significance was overshadowed by controversies of the time: 1) the Mini-Disc wascompeting for public attention with a digital audio cassette known as DCC—and the public did notseem to care much about either format; 2) the Mini-Disc used heavy audio compression to store
information on the disc, long before the public became comfortable with MP3 audio compression;and 3) the disc was housed in a protective cartridge. The Mini-Disc was not a recordable equivalentof a CD, and that is what consumers expected. So despite its many technological advances, theMini-Disc was only coolly accepted, except in Japan where it became a very popular product.
The cartridge or caddy holding the MiniDisc is square with sides of 7 centimeters (2 ¾ inches) and an
opening slide that makes the cartridge resemble a floppy diskette. The disc inside the cartridge
could be either a molded disc like a CD or a recordable disc. In many ways, the design of the discitself is very similar to that of CDs. The scanning velocity is the same 1.2-1.4 meters/second, and thetrack pitch is identical. The sampling frequencies are the same, as is the EFM (eight to fourteen)
signal modulation. The audio disc holds 160 megabytes, and the data format holds 140 MB withextra error correction. The biggest difference from the CD-R, other than the cartridge and the size ofthe disc, is the way the disc is recorded and the audio signal compression that is used on the disc.
Unlike CD-Rs that use a layer of photo-sensitive dye and CD-RWs that use layers of semi-metalalloys that react to the laser’s heat by either melting or crystallizing, the MiniDisc used a terbiumferrite-cobalt layer that worked in combination with both a heating laser and a magnetic head. The
laser heated the recording layer to the point at which it had no specific magnetic orientation (a Curie
point of 185° C or 365° F). On the other side of the disc at the same radial point is an electromagnetic head that magnetically records information to the surface of the recording just before thesurface cools and retains the magnetically printed pattern (Figure 17).

35

MiniDisc Magneto-Optical Disc
Magnetic Head

Magnetic Coating

Heating/Reading Laser

Gap between Head andDisc Surface

Figure 17

This type of recording format is known as Magnetic Field Modulation. Although this seems a step
backwards to the days of floppy disks, the change in magnetic patterns works in combination with areading laser according to a phenomenon known in physics as the Kerr Effect. The differingorientation patterns of the magnetic signals on the disc will change the polarization of laser lightreflected back from the disc in a way that is analogous to the pits molded into a regular CD or
MiniDisc. The laser is first used in a high-power mode of 6.8 milliwatts just to heat the disc from thebottom while the magnetic head does the recording on top. During playback, the laser reads thechanges in reflected light through the bottom of the disc in a way similar to that of the laser in a CD
player. The combined use of both a magnetic head and a laser also applied to other forms ofmagneto-optical recording such as M-O discs, but the MiniDisc is the most common use of thisrecording technology.
The diameter of the MiniDisc is only 6.4 cm (2.5 inches). The small size meant that the audio signals
had to be compressed in order to store enough music to make the format attractive.
Sony
introduced Adaptive Transform Acoustic Coding (ATRAC), one of the earliest forms of psychoacoustic reduction of digital audio data that was difficult to distinguish from the original
uncompressed signal. ATRAC used 16-bit stereo encoding at a sampling rate of 44.1kHz, but therate of data is reduced to one fifth that of a CD—just 292 kilobits per second instead of the CD’s 1.4
megabits per second. That data rate allowed 74 minutes of audio on the tiny disc, and further
developments increased the capacity to 80 minutes. This type of compression was considered
heretical to audiophiles when MiniDisc was first introduced, but it paved the way for MP3 and otherforms of sophisticated psycho-acoustic compression encoding that grew in popularity with the growthof the Internet and CD-R recording. A later version of the compression scheme called ATRAC3 witha bit rate of 66 kbps allows up to 5.5 hours of recording on a standard 80-minute disc and
ATRAC3plus at a rate of 48 kbps allows even more recording time.

36

Sony never gave up on its pioneering MiniDisc format, and continuing work has led to a 1-GB versionof the disc called “Hi-MD.” The Hi-MD disc competes with the miniature hard drives capable ofstoring 1.5 GB for use in portable audio players and digital cameras. Hi-MD recorders and playback
devices are backwards compatible in that they can record and play standard 60-, 74-, and 80-minute
MiniDiscs as well as the Hi-MD discs. Older MiniDisc equipment, however, will not be compatible
with Hi-MD discs.

DVD—MORE IS NEVER ENOUGH
Figure 1 showed the impressive increase of storage capacity of new media. Once the CD was wellestablished, researchers looked for ways to store high quality video onto a disc that same size.
Laser discs actually preceded CDs, but they were too big and held analogue video signals, notdigital. In order to fit the massive amounts of information that digital video required onto a CD-sized
disc, engineers worked to: 1) decrease the pit sizes by half from a minimum of 0.83 µm to 0.4 µm); 2)
increase the number of tracks (the number of rings the spiral on a disc can make) by reducing thepitch (the distance from the center of one track to the center of the next) to 0.7 µm, less than half thatfor CDs; and 3) decrease the amount of data required by throwing out unnecessary or repetitive
information. Figure 18 shows the result of engineering efforts to fit more pits into more tracks.
Two changes had to be made to for smaller data pits: 1) the wavelength of the reading laser
decreased from the 780 nanometer (billionth of a meter) wavelength used for CDs to 650 nm for
DVD; and 2) the discs had to be molded in two halves to get precise pit geometry and correct
focusing of the laser. 7 The two halves are then bonded together to equal the thickness of a CD.
Engineers even figured out how to make each half of the DVD hold an inner semi-transparent layer
to allow the laser to focus either on the reflective surface or the semi-reflective surface in the middle.
This allowed them to produce four different types: 1 side, 1 layer; 1 side, 2 layers; 2 sides, 1 layer on
each; and 2 sides, 2 layers each. Each version has a number code shown in Figure 19.
Figure 20 shows the different popular optical media and the basic manufacturing steps for each. It is
obvious that DVD is the most complex medium with its two bonded halves and potential semitransparent layers. (This form, however, offers great protection for the discs because the “top”
surfaces most susceptible to physical damage are glued face to face, unlike CDs and CD-Rs.) Just
as complex is the encoding of the video information. Professionals from around the world worked todetermine the best ways to compress video to render a high quality picture with a minimum of data.
They formed a Moving Picture Experts’ Group that issued a number of encoding schemes fordifferent applications. MPEG 2 is the format for DVD, and an audio compression scheme in layer 3
became the popular MP3 encoding. The video encoding provides a much more detailed picture than
VHS at a data rate that can fit a 2-hour movie on one CD-sized disc. DVD cannot provide HDTV or
7

See Figure 44 for a more detailed explanation of the focusing advantages of having two halves instead of a single piece of
coated polycarbonate

37

“high definition” TV at this point, but researchers are working on blue lasers with smaller wavelengths
than the red lasers used in CDs, CD-Rs, and DVDs as part of the solution as well as developing new
data compression schemes.

Figure 18

DVD Numbering
•
•
•
•

DVD 5
DVD 9
DVD 10DVD 18

4.7 GB
8.5 GB
9.4 GB
17.0 GBsingle side
single side
double side
double side

single layer
dual layer
single layer
double layer

Figure 19
The enormous capacity of the Digital Video Disc attracted CD-ROM users who wanted encyclopedias on one disc instead of 6
or more CD-ROMs and audiophiles who wanted higher resolution audio than CDs provided. So the DVD acronym was officiallychanged to mean “Digital Versatile Disc.”38

Optical Media
Protective lacquer

CD-R

Reflective layer

CD

DVD

Organic dye
Polycarbonate plastic
Adhesive

=1

=0
laser

1)

optical pickup

Mold base with ATIP info & wobbled
groove2)

Spin-coat with dye

3)Sputter reflective silver or gold on dye

4)Clean edges

5)Spin-coat lacquer on top of silver or
gold

1)

Mold base with data

1)

Mold base(s) with data

2)

Sputter aluminum onto base2)

3)

Spin-coat lacquer onto
aluminum

Sputter aluminum onto
base

3)

4)

Silk-screen surface

Spin-coat lacquer onto
aluminum

4)

Glue 2 bases together

Figure 20

DVD-RECORDABLE FORMATS—MORE THAN 1 IS TOO MANY!
The same question that followed CDs followed DVD—when can we record on them? The answer
came with several competing formats offering the ability to record high-density data on a disc that
may or may not be playable in a DVD player. The reasons for the competition are due to a
combination of corporate pride, economics, technical arguments, and political resistance.
•
•
•

•

Corporate pride—the developer of the “winning” format will have the reputation for ingenuity
and marketing savvy. Ego drove Sony and JVC to a horrific battle over home video that JVC
eventually won in the marketplace with its VHS system.
Economics—the media industry is famous for price erosion so severe and sudden that thebest chance for profit is not in manufacturing but in the royalties based on patents. Eachdeveloper is pushing for his format to provide that kind of profit protection for the future.
Technical arguments—video generally requires a long stream of data; data storage requires
fast random access. Developers of the first two systems concentrated on one requirement or
the other in their designs. A third, later group was able to combine both requirements in its
system.
Political resistance—the music industry has put up a losing battle with CD-R, MP3, and copy
protection. The motion picture industry has much greater firepower, and it wants to be
assured that no one will be able to illegally copy and distribute movies on these new media.

At this point there is no clear answer as to which format may be the clear choice for most users orwhether all the formats will continue to coexist. Each of the formats is different for one or more of thereasons above.

39

Optical Disc Capacities
Unformatted
Formatted
650 MB
650 MB
700 MB
CD-RW
650 MB533 MB
700 MB572MB-5
4.7 GB*-9
8.5 GBDVD-10
9.4 GB-18 17.0 GB
DVD+/-R
4.38 GB
4.37 GB
DVD-/+RW
4.38 GB
4.37 GB
DVD+/-R DL 7.96 GB
2.6 GB
2.32 GB
DVD-RAM
4.7GB*
4.2 GB
5.2 GB
4.6GB
9.4 GB
8.4GB
CD
CD-R

Audio min.
76 minutes
74 minutes
80 minutes

Video min.
1 hour (MPEG 1)
1 hour (MPEG 1)

133 minutes (MPEG 2)

1-13 hours**
1-13 hours**

1-6 hours

Figure 21*This figure is actually 4.377GB because the DVD Forum defined 1 GB as a billion bytes in the decimal system instead of the conventional binary
system of 1,073,741,824 bytes (230) that computers recognize.
** Windows 95 will only allow a file up to a maximum of 2.0 GB; Windows 98 allows a maximum of 4.0 GB; XP has removed limits on file sizes.
These numbers generally correlate with the 4.377GB capacity of a DVD disc, but inconsistencies remain in both software and operating systems.

DVD Recordable Overview
CD-R

DVD-R

DVD+R

DVD-RAM
rewritable

DVD-RW
rewritable

DVD+RW
rewritable

Laser
wavelength

780 nm635/650nm

650 nm

650 nm

650 nm

650 nmRecordingmethodOrganic
dye

Organic
dye

Organic dye

Phase changesemi-metal alloy

Phase changesemi-metal
alloy

Phase changesemi-metal
alloy

Track
structure

WobbledspiralgrooveWobbledspiralgrooveWobbledgroove withland pre-pits

Pre-molded pits
along concentric
grooves

Wobbledgroove withland pre-pits

HF modulated
wobbledgrooveRecordingarea

In grooveIn grooveIn groove

In both groove
and landIn grooveIn groove

Number oferases000Class 0: 100,000
Class 1: 10,000

1,000

1,000

velocity

CLV/CAV

CLV

CLV/CAV

CLV/CAV

CLV

CLV/CAV

recording
speed range

1x - 52x

1x - 16x

1x - 16xClass 0: 1x– 5xClass 1: 8X-16X

1x - 2x ver.1.1
1x-4x ver. 1.2

1x - 4x3.3x-8xDesignobjective

audio

video

Audio/video
data

data

Video

Audio/video
data

Figure 2240

DVD-R
DVD-R is very similar to the CD-R in its design and function. The original design objective was toprovide a recordable disc that could hold enough video information to compete with VHS video
cassettes in terms of capacity. Like CD-Rs, information is recorded in a groove filled with an organic
dye; and once the laser alters the dye, the information cannot be changed. The disc rotates atdifferent speeds so that the data pass under the laser at a constant rate. This rate is called CLV, or“constant linear velocity,” meaning that the groove travels as a steady line no matter whether it islocated toward the inside of the disc or toward the outer edge. If the data are on the outer edge, thedisc slows down to keep the rate of reading the data the same as the reading rate toward the center
because, like a wheel, the outer edge turns faster than the inner edge around the spindle. CDs and
CD-Rs also use the CLV design. Figure 23 shows a cross section of a disc groove with the laser
mark fitting in the groove itself.
In order to provide copy protection for copyrighted video programs, the developers of the DVD-R
offer two different versions. One is for “general” use, and it uses a 650 nm laser wavelength forrecording. This wavelength is identical to that used in DVD players so consumers who record home
videos can transfer them to general use DVD-Rs and play them in their DVD players. “Authoring”
DVD-Rs are those used to make video masters on sophisticated hardware unencumbered with copy
protection schemes that could present software conflicts during video programming. The authoring
discs use a 635 nm laser wavelength to distinguish them from the general use versions. These discs
can also be played on DVD players, but they cannot be recorded in general use drives. Eachgeneral use disc is actually recorded in special DVD recorders immediately after manufacturing in aprocess called “pre-writing.” Identification codes unique to each disc are written in the Control Data
Zone reserved in the lead-in section of each disc. This special track is often visible as a 0.1mm track
closest to the center hub. These codes block the direct copying of DVD discs protected with the CSS(Content Scrambling System).
The first “consumer” DVD-R drives could record at 2X for only a few DVD-R discs. All others wererestricted to 1X speeds. By the time 4X drives appeared, the number of disc suitable for 4X
recording had increased dramatically, but these 4X discs posed a larger problem for older drives:
unless the drives’ firmware is updated, a 4X disc is likely to lock the drive in a recording cycle that
could burn out the recording laser unless the user intervenes to stop it. Pioneer and suppliers of 4X
discs warned users about the potential problem and offered a firmware update to resolve theproblem. Shortly after 4X DVD-R discs appeared, most DVD-R drive manufacturers, including
Pioneer, introduced “dual” DVD recorders that could record on both DVD-R/RW and DVD+R/RW.
The general purpose DVD-R discs offered in the U.S. (version 2.0) 8 have a pre-formatting address
scheme in the form of “land pre-pits” between the grooves to identify data blocks, a pre-recorded
control area that prevents bit-for-bit copying of CSS encrypted movies, Content Protection for
Recordable Media (CPRM), and the possibility of double-sided discs. One reason for the use of the
650 nm laser is its lower cost so that “general” use drives do become more affordable. The latest
version of the authoring DVD-Rs, version 2.0 /4.7GB, reserve space in their lead-in area for DDP(Disc Description Protocol) header information that is commonly used on DLT master tapes for DVD
8

Version 1.0 was only 3.95GB when it first appeared in 1997. Version 1.9 in 1999 increased capacity to 4.7GB, and thenext year DVD-R split into the authoring version 2.0 and the general use version 2.0 common today.

41

replication. This feature, known as CMF for cutting master format, allows the authoring DVD-R discs
to become direct replacements for DLT masters. General-purpose discs cannot be recorded on
authoring drives, and the authoring discs will not work on general-purpose drives. Once recorded,
however, the discs can be played on each other’s drives and on most recent DVD players or DVDROM drives.

DVD-R Disc Structure
polycarbonate
Top half of discBonding layer
Lacquer
Reflective layer
Recording layer
polycarbonate

Laser beam
In disc groove

Figure 23

DVD-RW
The erasable and rewritable DVD is similar to the CD-RW version in its basic design, and its
operating parameters are directly related to the DVD-R. The marks the recording laser leaves reflect
the light at a different angle from the unmarked portion so that the marked reflection misses the
optical sensor just as if no light came back at all. This design is known as a “phase change” of thelight, and all of the rewritable DVD systems use this method. Like CD-RW alloys, the alloy used in
DVD-RW may have trouble reacting predictably to the laser power after 1,000 cycles; so that figure isused as the upper limit of record/erase times. The lower reflectivity of the DVD-RW can cause
confusion in some DVD players and DVD-ROM drives that mistake the disc for a dual-layer DVD andstruggle to read it. Other drives may not recognize the disc format code of the DVD-RW and refuse
to play it. Drives that may accept the DVD-R may not accept the DVD-RW unless their firmware canbe brought up to date. The latest DVD players are becoming more compatible with DVD-R and
DVD-RW discs. The first versions of DVD-RW discs have a speed rating of 1X-2X and are known
as “version 1.1.” DVD-RW discs capable of 4X or even 6X recording speeds are known as “version
1.2” and cannot be recorded on older recorders. User manuals for set-top recorders note thedifference but often explain it in a way that makes it difficult to understand.

42

The DVD-RW was introduced as a video alternative to the rewritable DVD-RAM. Video recordings
on DVD-RAM cannot be played on regular DVD players even if the discs are removed from theircartridge (see below); so DVD developers wanted an erasable DVD medium that could be reused
just as video tape can be. The DVD-RW works well in that role; but when used for data, its video
parentage becomes a problem. Video recordings are generally sequential: new video as added at
the tale end of earlier recordings. The sequential design, however, prevents data from being erased
from the DVD-RW to allow more room in their place. Deleting files from a DVD-RW will not increase
the disc’s capacity. The only capacity available is that at the end of the last section of recorded
information. This is a handicap only for data, not for video; but some DVD developers weredissatisfied with this limitation and wanted a format that worked equally well with video and data.
Their solution was the DVD+RW below.

DVD-RW Disc Structure
Polycarbonate upper half
Adhesive
Top half of disc2P resin
Reflective layer (Al alloy)
Protective layer(ZnS-SiO2)

Recording layers
Protective layer

Laser beam
In disc groove(In-Ag-Sb-Te)(ZnS-SiO2)

Polycarbonate

Figure 24

DVD-RAM
This DVD is the most unusual of the recordable DVD discs. It is designed for Random Access
Memory (the RAM in the name), a way to find and get data very quickly. The design offers a great
deal of memory storage capacity for data files, and its original intended use as a data storage andback-up medium got around the problems associated with video copy protection although the discs
can also be used to record video. In addition to concentric grooves (like data tracks on a hard drive)
molded into a slice of polycarbonate that is bonded to a second slice, there are also pits used to
identify sectors for address information so that a drive can locate files very quickly. These molded
addresses are visible on the DVD-RAM discs as a series of small lines perpendicular to the centeringhub. Additional addresses appear every 2kb just before user data so access is extremely fast.
Recording is done in both the grooves and the land between the grooves so that the grooves can bea bit wider without reducing total recording capacity. The disc turns at the same rate of speed all the43

time, a rate referred to as CAV for “constant angular velocity.” 9 This design feature also aids data
access speeds because the spindle’s servo motor does not have to take time to change speeds.
The most unusual aspect of the DVD-RAM is that it is often enclosed in a protective cartridge.

Safety plug/sensing hole

Write/protect lock

DVD-RAM Types:
Type 1: non-removable discs of all capacities
Type 2: single-sided removable discs
Type 3 single-sided bare discs
Type 4: double-sided removable discs
Type 5: double-sided bare discs
Type 6: double-sided removable 8-cm discs
Type 7: single-sided removable 8-cm discs
Type 8: double-sided 8-cm bare discs
Type 9: single-sided 8-cm bare discs

Figure 25
The Type 1 DVD-RAM versions cannot be removed from the cartridge, but Types 2 and 4 cartridges
do allow the discs to be removed if the user is very careful. The cartridge prevents the use of DVDRAM discs in DVD players; but since the original design objective was to provide a high capacity
medium for data storage, not home video recording, the limitation may not be important in themedium’s intended market. The design of DVD-RAM, however, does give it a unique advantage forvideo: DVD-RAM drives can simultaneously write and read from DVD-RAM media. This allows auser with a set-top video recorder to watch a program while recording it, leave to answer a phone
call, then return to catch up watching the portions of the program he or she missed while the recordercontinues to record without a break. DVD-RAM also offers the advantage of being able to withstand9

Panasonic refers to the speed as “zoned CLV,” meaning that the drive does change speeds to some degree dependingon where it expects to find data addressed in a particular zone of the disc. Because the format design is to provide fast,
random access for data, there is a defect management system built into the drive to avoid using areas of a disc it finds
suspect. The DVD-R, because of its design objective for video, is best at linear recording. DVD-RAM allows faster accessto and retrieval of data.

44

100,000 record/erase cycles, a feature that is essential for a medium intended for frequent updates,
high storage capacity, and random accessibility, or as a video recorder for time delayed viewing.
The double interface layers in the coating allow the greater number of erasures and rerecordings
compared to CD-RW, DVD-RW, and DVD+RW discs. (DVD-RAM discs rated faster at 8X or faster,
however, are capable of only 10,000 cycles instead of 100,000 cycles for the slower discs.)
The DVD-RAM cartridge is somewhat similar to that of a micro floppy disc with a sliding shutter
protecting the medium inside and a write/protect lock on the lower left side of the cartridge. The
removable discs have cartridges with a knockout plug holding the hinged door in place. Once theplug is removed, the remaining hole becomes a sensor hole to tell a drive that the disc had been
removed at one time. The drive firmware may then identify any errors as due to a dirty or damaged
disc or may verify all data that are subsequently written to a disc that had been removed. DVD-RAM
discs are also available without cartridges. There are two classes of bare discs: Class 0 for speeds of
1X, 3X, or 5X recording speeds and Class 1 for 6X, 8X, 12X, or 16X recording
speeds. Drives compatible with Class 1 media can write and read both Class 1
and Class 0 discs, but older Class 0 drives cannot record Class 1 discs and may
have some trouble reading them.
The protective cartridge, built-in sector addresses, error management, and ability for multiple
erasures and rewrites make DVD-RAM an excellent medium for reliable data back-up and retrieval.
These very features, unfortunately, make the format less than ideal for exchanging video recordings
on DVD players.

DVD-RAM Disc Structure
top half of discBonding layer
Lacquer
Reflective layer
Optical compensated layer
Upper dielectric layer
Interface layer
Recording layers
Interface layer
Lower dielectric layer
Polycarbonate

Figure 26

Laser beamin disc groove

DVD+RW
There is an advantage in following others—one can recognize and address any of the pitfalls
discovered by those who went before. The third version of recordable DVD is called DVD+RW to45

distinguish it from the DVD-RW that Pioneer introduced. This medium tries to provide all the features
and advantages of both DVD-RW and DVD-RAM in a single disc format. (See Figure 22). It canoperate at either CLV or CAV speeds, depending on whether or not the information is audio/video ordata stored in the planned Mt. Rainier format. It can apply defect management systems whenrecording data or can leave them off when recording video so that DVD players can recognize thediscs. Recorded discs can be played in about 80% of existing DVD-ROM drives and DVD players if
the video is recorded in the DVD-Video format. The more recent the player, the more likely it will
successfully recognize and play the disc.
DVD+RW has some significant advantages that are due to its formatting structure. The structure isbased on an 817-kHz wobble incorporated into the groove molded into the polycarbonate base. This
wobble is 37 times finer than the wobble in a CD-R, and the detailed waveform it provides makesaligning data blocks much easier and more accurate because it serves as the disc’s addressing
system. The fine detail in the signal allows “lossless linking,” meaning that adding to or erasing
information from a DVD+RW disc can put new data no more than a micron gap away from existing
information because the ultra-high frequency wobble acts as an accurate marker guide for therecording laser (Figure 34). That built-in accuracy provides some very significant advantages for
DVD+RW: 1) fully erasing and formatting the disc takes less than a minute compared to the 87
minutes required by DVD-RW with early software because DVD+RW allows “background formatting”(the formatting process continues as the computer moves on to other operations; formatting does notmonopolize the computer as it does for DVD-RW); 2) it becomes very easy to make edits directly to a
DVD+RW disc for video recorded in the VR format; and 3) the total time to record and close a disc is
less.
The DVD+RW and DVD+R discs use an address system referred to as ADIP (“ADdress In Pregroove”) that is different from the DVD-R and DVD-RW discs’ land-prepit address system. In CD-Rs
the ATIP area contains the address information as well as information about the type of disc; themodulated groove provides tracking information as well as the correct read speed based on thefrequency of the wobble in the groove. The DVD-R/-RW format also uses a groove modulated at a
relatively low frequency of 140.6kHz for tracking and speed information; the LLP (land-prepit) data
provide the addresses via data signal spikes as the laser reads the groove. DVD+R/+RW discs havea groove modulated at a much higher rate of 817.4kHz with address information provided by phase
inversions in the signal. The phase inversion takes place over a longer section of the disc that is 32
times larger than the smallest land pre-pit signal (32T versus 1T), and that makes it easier for a highspeed device to detect the address information of a phase-inverted DVD+ signal than that for a small
DVD- signal spike caused by a land pre-pit.

DVD+R
DVD+R is a dye-based version of the DVD+RW that followed the introduction of the +RW by half ayear. (This presented a problem for early adopters of the DVD+RW drives who expected their drives
to be able to be upgraded with simple firmware changes so that they could write on write on DVD+R
discs as well as DVD+RW discs. The final DVD+R design, however, meant completely new drives.)
The similarities of DVD+/-R and DVD+/-RW are so strong that the pictures of DVD disc structures46

that appear in figures 20 and 21 can apply to both DVD+R and to DVD+RW as well as to DVD-R and
DVD-RW. The formats differ in terms of file structure and the design of the groove pressed into thepolycarbonate substrate more than in their physical construction and materials. The dye-based
DVD+R, like the dye-based DVD-R version, is more compatible with existing DVD players than theirrewritable partners chiefly because the reflectivity of dye based media is much greater and similar tothat of pressed DVDs. The lower reflectivity of the rewritable DVDs can confuse many DVD players
into treating them as dual-layer discs and not being able to read them. Unlike DVD-R discs whichmust be individually recorded after assembly with a track to block DVD copying of CSS-protectedmaterial, DVD+R discs are complete after assembly.
There are claims and counter claims about whether or not DVD+R discs are more or less compatible
with DVD players than DVD-R discs. Based on the number of claims, the best judgment is that there
is little difference between the two in terms of compatibility. DVD-RAM recorders and players built by
DVD-RAM supporters are more likely to play DVD-R discs than DVD+R discs, but there is little realdifference between the two in terms of compatibility or capability. The real distinctions between the“plus” and “dash” camps lie in the rewritable DVD-RW and DVD+RW, not in the write-once discs.

DVD-VR AND DVD+VR
These two terms do not describe new formats but “formats within a format,” or as the DVD Forumdescribes DVD-VR, “an application format.” They have been introduced to allow set-top DVD
recorders to record video in real-time, for example, from TV broadcasts received on built-in TV
tuners. The original DVD specification requires certain data to precede the writing of video
information. Parameters describing file lengths and navigational information such as menus—thetype of information that DVD authoring software handles—is supposed to be written first on a disc.
When recording data from a TV broadcast, however, the full amount of information is not known until
the recording is finished. DVD-VR and DVD+VR manipulate the data in a way that allows“streamed,” that is, real-time recording to continue so that the necessary “preliminary” data can be
written afterwards when the disc is finalized. This data manipulation also allows some limited video
editing, deletion of video segments, and modifications to the play lists on rewritable discs. The
approach each application format takes is different and applies only to the like named DVD discs.
DVD-VR is designed for DVD-R and DVD-RW discs in set-top recorders. Its editing features are a bit
more extensive than those for DVD+VR, but that advantage comes at a cost: DVD-R/-RW discs
recorded in the DVD-VR format will not play in any other DVD player except the recorder itself.
Some DVD players may be introduced to play these discs back, but the number of DVD-VR-capable
players that exist now is so small that it is more reasonable to consider playback impossible.
DVD+VR applies to DVD+R and DVD+RW discs in set-top recorders. Its distinguishing feature isthat it creates thumbnails for menus in the title page instead of the DVD-VR play lists, and thethumbnails can have titles applied to them. There are some other limited editing abilities thatrecorders may incorporate, but DVD+VR gives up sophisticated editing in favor of DVD video
compatibility. Almost every DVD player that can play DVD+R/+RW discs will also play DVD+VR
formatted discs. They are not restricted to the recorder that created them, unlike DVD-VR formatted
discs.

CPRM (CONTENT PROTECTION FOR RECORDABLE MEDIA
CPRM is a copy protection scheme that will allow a user to make one and only one copy of an
encoded analogue program. The scheme requires a recorder and disc that are both capable ofinterpreting the CPRM signals. CPRM-capable discs have decryption data recorded in the burst cut
area including a media identification number unique to each disc. CPRM-capable recorders havedevice keys in their memories that combine with the CPRM disc data to allow recording of a CPRMencoded broadcast and mark the disc as “cannot copy” once the recording is complete. No copies

47

can be made of the encoded disc. Discs that do not have the CPRM data on them cannot be used in
CPRM recorders to record any broadcast that is encoded with the CPRM signal; only CPRM-capable
discs would work for such broadcasts.
CPRM decryption data are only used on DVD-RW and DVD-RAM discs and is only used forrecording in the VR mode, that is, the Video Recording mode used to record from analogue
broadcast signals. CPRM is not used in either Europe or the Americas yet, but set-top recorders thatcan record either DVD-RW or DVD-RAM are already compliant with CPRM encoding.
In the U.S. the Federal Communications Commission has approved a system that by the year 2005
will include a broadcast “flag” in digital programs that restrict recordings at the option of thebroadcaster. In anticipation of this change, Philips and HP have proposed a system somewhat
similar to CPRM for DVD+R/+RW discs tentatively called “Vidi.” This proposal also requires
information to be in place in the ADIP section of DVD+R/+RW discs as well as compliance in thecircuitry of the recorders.
DVD recordable discs come with a new set of acronyms and test parameters. Some of them are similar to
those used in CD-R/-RW testing, but most are descriptive of the special characteristics of DVD recording. The
following list describes the most commonly used terms.
ASYM
FE
I3/I14
LPPb
PIE
POE
PIF
POF
PPb DV
PWP
RRO

Asymmetry
Focus Error
The signal from the shortest pit/land distance (3T) and the longest (I14)Land Pre-Pit before recording
Parity Inner Error
Parity Outer Error
Parity Inner Failure
Parity Outer Failure
Push-Pull before recording Disc Variation
Phase Wobble Pre-pit
Radial RunOut

ASYM
Asymmetry is the DC offset voltage difference between the I3 and I14 signals (the shortest and the longest
signals; see below). Values are measured as both an average and as a maximum. Values <3% indicate a
uniform coating of the dye layer. Changes >10% indicate coating problems that vary the I3 and I14 signals
enough to cause read errors when the analogue output signal is converted to a digital signal.
FE
Focus errors are the result of sectors not being addressed properly due to buffer underruns, impurities in thecoating, or uneven substrate. Focus errors produce indefinite write marks that raise jitter values and the rate ofread errors. Radial 2 measures radial disturbances in a frequency range of 1.1 and 10 kHz and refer to thetracking signal of a recorded DVD. Radial 2 disturbances are beyond the ability of the servo control to correctbalance and are a factor in read errors.
I3/I14The shortest pit or land has a value of 3; the longest pit or land has a value of 14. As the light from the reading
laser varies according to the length of lands and pits, the signals generated from the shortest lands/pits, I3
signals, change at the highest frequency rate while the I14 signals form the longest lands and pits have thelowest frequency of changes. All the signals from I3 to I14 create an analogue signal that is converted into a
digital signal representing the information on the discs. I3 signal values should be above 0.45 for a strong
output. Values below 0.3 are poor signal levels. I3 has such a short distance between pit/land/pit orland/pit/land that signal levels are low and difficult to resolve. I14 Signals above 2.0 are very good while thosebelow 1.5 are quite poor.

Jitter48

The lengths of the lands and pits should be kept as exact as possible—perfect multiples of IT signals. In
reality, the lengths show variations in their actual lengths that translate into timing variations referred to as jitter.
DC jitter (data-to-clock jitter) is a measure of the length of each pit and land against the precise measure of aclock pulse time signal. DC jitter is measured over theentire disc and should measure below 9.5%. Bottom jitter is the value at three different points on the disc as
seen by the laser. If bottom jitter is quite different from DC jitter, that is an indication that the disc hasmechanical distortions.
DC jitter is also dependent on the write strategy of the burner. If the incorrect write strategy is applied, DC jitter
increases as well as PI sum 8 values and the uncorrectable POF errors.

LPPb
DVD+R/+RW discs use the 817-kHz wobble signal in the groove to address sectors, but DVD-R/-RW uses land
pre-pit “bridges” at the beginning of each sector. If the signal from the pre-pits is too weak, the drive cannot
identify the pre-pits; if the signal is too strong, it can disturb the data signal.

PIE/POE
DVDs have double error correction. Drives put 16 sectors (sector = 2,048 bytes of usable data + 308
bytes of error correction + 4 bytes for the sector ID + 6 bytes for copyright management = 2,366 bytes) ofusable data into an ECC (Error Correction Code) matrix. The rows of the matrix are checked for accuracy
according to “inner parity” while the columns are checked for “outer parity.” This two-dimensional error
correction is nearly 10 times more efficient than that for CDs and can correct severe flaws caused by scratches
or debris as large as 6 mm. The DVD specification requires that the sum of PIE in 8 sequential ECC sectors(PI sum 8) be less than 280.
DVD+R specifications require that after the first PI correction no more than 4 errors remain in the ECC sector
for the sum of Parity Inner Failure. These should be corrected by the second error correction so that no errors
remain for Parity Outer Failure. If POF is >0, the errors will be noticeable.

PPb DVThe push-pull signal from the drive assembly holds the laser in the track during burning. The difference
between the strongest and weakest push-pull signals must be as small as possible to avoid problems following
the track. These differences are measured as variations in the signal.

PWP
The land pre-pit signal must be -90º out of phase with the wobble signal. The pre-pit signal can deviate amaximum of +/- 10º for the Phase Wobble Pre-pit measurement.

RRO
Radial runout is the deviation of the pre-groove spiral in the substrate from the ideal distance from the center ofthe disc. It is a measure of the difference between the maximum and the minimum distance of a physical trackfrom the axis of rotation measured over one revolution.

RECORDABLE DVD CAPACITIESThe standard DVD is capable of providing 4.7 GB of storage on one side of a disc with a single layer.
One would think that this enormous capacity in a single disc would satisfy anyone used to the 1.4 MB
capacity of the common double-sided, double density floppy diskette. But even the name of thatmodest medium gives the story away: it was the successor of an original single-sided, standard
density diskette that had replaced the 5.25-inch floppy that had replaced an 8-inch version. The
design goal is always to provide more storage capacity in a smaller medium so that the cost per
megabyte decreases. People will find a way to use all that storage space, and then ask for more.

49

Figure 27 is an example of how quickly data capacity gets used. Figure 28 charts the amount of dataneeded to store or move information. Too much is never enough!
Expressing file sizes
Computers calculate in binary form; humans calculate in decimal form because of our 10 fingers. Even though“digital” comes from the Latin word for finger, digital data are calculated as binary amounts. The difference has
led to a great deal of confusion over capacities. The numerical expressions for the large amounts of data use
prefixes from Latin and Greek decimal numbers. When applied to binary numbers, these terms are notaccurate because the binary numbers are always slightly greater than the decimal expressions. As thenumbers grow in value, the difference becomes larger. Computers express file sizes in binary terms. Storage
media such as drives, optical discs, and flash media generally use the decimal method according to thestandard recommended by IBM in the 1950s. The difference in value was of little significance then, but ascapacities have grown, the difference has also grown:
CommonTerm

Greek
Prefix

Original
Meaning

Literal decimal
meaningkilobyte
megabyte
gigabyte
terabyte
petabyte
exabyte

kilo
mega
giga
tera
peta
exa

“thousand”
1,000
“big”
1,000,000“giant”
1,000,000,000“monster”
1,000,000,000,000“five”
1,000,000,000, 000,000“six” 1,000,000,000,000,000,000

Value in Binary Terms

Suggested change
Difference for Binary Values

1,024
1,048,576
1,073,741,824
1,099,511,627,776
1,125,899,906,842,620
1,152,921,504,606,850,000

2%
5%
7%
10%
13%
15%

kibibyte
mebibyte
gibibyte
tebibyte
pebibyte
exbibyte

The difference is most obvious when one compares the stated capacity of some storage media with thecomputer’s calculation of that capacity. A “10GB drive,” for example, may have 10 billion bytes of storage
capacity, but the computer will divide by 1,024 to determine the number of gigabytes rather than by 1,000; so it
will claim capacity to be 9.3 GB, not 10GB. A 4.7GB DVD holds almost 4.7 million bytes of data, but in binary
terms that is a mere “4.37GB.” Some groups have called for new terminology to define the “kilo binary byte” asa “kibibyte” to distinguish it from a decimal “kilobyte” in order to reduce the confusion. The last column above isthe proposed list of new terminology to distinguish binary values. Others, ignoring the heritage of IBM, Greece,
and nature’s ten fingers, have claimed the storage industry is cheating the consumer because the computer isalways right. The difference between stated capacity of a medium and what the computer claims it to be iscompounded by formatting that takes up some of the capacity of rewritable media. They need to reserve someof their capacity for file addresses and error correction, and the media cannot be used unless they areformatted with that information first. The amount of capacity taken up varies according to the software used toformat the medium, but it can be a significant portion of total medium capacity. This reference guide will referto the stated capacity of storage media in order to keep things as clear as possible.

DVD-Recordable Capacities
4.7 GB are equal to:
–
–
–
–
–

4,700 full-color pictures (640x480 resolution; 24-bit
pixels)
210 minutes of compressed MPEG-2 video (at DSSsatellite quality)
60 minutes of theater-quality MPEG-2 video
Nearly 9 hours of CD audio
400,000 plus documents (filling eight 4-drawer filingcabinets)

Figure 2750

Growth in Data Requirements
kilobytes

1 page ASCII text

35,00030,0001-page FAX

25,00020,00034,8001-page color image
15,0001 minute CD audio

10,0005,000

1 minute DVD video

3

50

5,000

8,780

0

Figure 28

CAPACITY IN TERMS OF TIME
4.7GB means nothing to most people looking to record TV programs on their DVD set-top recorders.
Capacity for them is the number of minutes or hours that a disc can hold. VHS tape had three time
settings: SP for standard play of 120 minutes for a T-120 or 180 minutes for an E-180 in theEuropean PAL TV system using an almost identical cassette. LP was “long play” for 4-hour
recording in North America and 6-hour recording in Europe. The EP or SLP settings (“extended play”
or “super long play”) increased tape capacities to 6 hours and 9 hours, respectively. The video
quality, of course, declined for the longer time settings because the amount of video signal per
minute of tape decreased in order to store more video on the tape. The same holds true for digital
video recording on DVD discs: the amount of video data per minute of video has to be decreased inorder to fit more time on a disc. The rate of data is referred to as the “bit rate.” DVD-compliant discs
can hold a maximum bit-rate of 9.8Mbps (megabits per second), for both audio and video signals.
Software programs often allow users to select a bit rate from about 8mbps for “highest quality” toperhaps 4 Mbps for lower quality but increased capacity. Set-top DVD recorders do the same thing,but they refer to quality levels in terms of minutes or hours of recording time.
The good news is that the time limits are identical for the North American NTSC video system andthe European PAL system. Unfortunately, the designations are not consistent from format to format
or even from manufacturer to manufacturer. Figure 28 lists the different capacities for the various
formats in terms used by the consumer set-top recorders.
Bit rate settings can be either a constant, unchanging rate (CBR or constant bit rate) or variable(VBR). The variable rates assign more data to complex video with lots of detail and action and lessdata to simpler video in order to maintain good picture quality and an efficient use of capacity.
People expect to see better quality on DVD than that from VHS tape, and that is always the case with
Hollywood movie releases. Video recordings on DVDs, however, depend on the bit rate settings aswell as the quality of the encoders converting video to the DVD MPEG-2 standard. Hollywood uses
equipment and software that cost in the hundreds of thousands of dollars, and the quality is
excellent. Home video, however, relies on far less expensive chipsets. Many people have been
disappointed to see DVDs made from home VHS tapes look slightly inferior to the original tapes evenwhen using the highest quality settings. The difference in quality is due to encoding, not to themedium. Even MiniDV digital video cassettes (encoded at 25Mbps) will look slightly inferior whenconverted to DVD settings of 9.8 Mbps or less. Set-top recorder settings longer than two or three51

hours often display the most visible forms of picture deterioration. VHS video tape suffered fromlower resolution, greater noise, and more visible dropouts at the longest EP time settings; DVDs
recorded in the DVD EP mode also show lower resolution and digital artifacts such as pixelation andblocking (“stair-step” edges on diagonal lines and odd rectangular shapes in the picture). Many
people find the decrease in quality of DVD EP to be worse than that of VHS EP. The solution is to
use the highest bit rate possible or the shortest time setting to get the best balance between video
quality and time capacity.

Set-Top DVD Recorder Capacities(NTSC and PAL)

RECORDER

TYPE OFDISC

RECORDING 60 MIN 120 MIN 180 MIN 240 MIN 360 MIN 480 MIN 600 MIN 802 MIN
4 HR
6 HR
8 HR
FORMAT
1 HR
2 HR
3 HR
10 HR 13.3 HR

DVD-RAM

DVD-RAMUDF 2.0

XP

SP

LP

EP

EP

DVD-R

DVD Video

XP

SP

LP

EP

EP

DVD-R/-RW

DVD Video

XP

SP

LP

EP

SLP

DVD-RW

VR format*

DVD-RW

MN-format

Pioneer
DVD-R

DVD+R

Figure 29

DVD+R/+RW DVD Video

SEP

VR-SP
level 32level 21level 15level 9

HQ

SP

LP

EP

level 1EP+

SLP

Incompatible with regular DVD players; playable only in the same type of recorder.
*VR means "Video Recording"; MN means "manual" with 32 manual rate settings from 61 to 802 min.

DL DOUBLE-LAYER DISCS
There never seems to be enough storage capacity for our growing number of audio, video, and data
files. In the battle for the next generation of optical discs, the Blu-ray camp has put most of its
arsenal in its boast of extra capacity despite the complexity of its design. In the meantime, DVD disccapacities can be extended beyond the standard 4.7GB in one of two ways: double-sided DVD discs
or double-layer discs. Here too, despite the fact that double-sided discs are easier to manufacture(All DVD discs have two halves; the top half is just a blank.), the emphasis has been on the more
complex double-layer discs. The DVD+R DL (known as “double-layer” to avoid confusion with “dual”
format drives) recordable disc was the first to appear. DVD-R DL (known as “dual-layer” just to bedifferent) followed not long after. Just as in double-layer DVD-9 video discs, the technique uses a
semi-transparent silver alloy metal mirror layer and a spacer sandwiched between two layers oforganic dye. This metal reflector layer has a reflectivity of 18%, similar to the middle mirror layer indouble-layer DVD-9 discs. The middle dye layer itself (L0 in Figure 30 below) has a lighttransmission value of 50% to allow the laser to penetrate it to the L1 dye layer above it. The L1 dye
has to be much more sensitive to the laser power than the L0 dye because so much laser light isscattered and absorbed while passing through both the semi-transparent silver layer and the first dyelayer below. The reflectivity of the metal layer for L1 is greater than 50%, but it ends up also at about
18% after the reflected light passes through both dye layers and the semi-reflective alloy layer. The
length of the data pits increases about 10% for easier reading, and that is why the total capacity of adouble-layer disc is slightly less than twice that of a 4.7GB single layer disc. Careful tuning of thedyes, metal deposition, and groove geometry has resulted in a double-layer disc with 8.55GB of
storage capacity, but not without some tradeoffs.
Double-layer discs require double-layer drives in order to be recorded, and DL recording speeds are
slower than those for single-layer discs. The initial double-layer drives wrote at 2.4X for DVD+R and

52

Picture courtesy of Philips

Figure 30
4X for DVD-R, but their lasers had power ratings equivalent to those for 8X discs because more
power is required for the light to penetrate the semi-transport layer and the spacer layer. 16X DL
recording requires 350 milliwatts of power or more for recording.
Since a laser reading or writing a double-layer DVD starts from the inside and works outward on the“outer” layer (layer 0) to a transition point where it refocuses and switches to the “inner” layer (layer1), both layers have to have data signals matching in their total length in order to prevent DVD
players from seeing errors. Dividing fixed files into two equal sizes is not a problem for computer
systems, but recording video broadcasts that are not exactly defined can pose a problem for set-top
recorders using the VR mode designed for flexible recording undetermined amounts of video. In
figure 31, for example, the 7-GB disc recorded in a computer drive only records half of the 7.0 GB on
L0 and moves on L1 before reaching the outer edge of the disc. Recording a two and a half hour
program in the VR mode on a home video recorder also uses only a portion of the disc, but therecording goes to the outer edge of the L0 layer because the recorder does not know how much isgoing onto the disc in the VR format. It simply maximizes the amount that can be recorded. If thedisc is finalized at 2.5 hours instead of the full 4 hours in the SP mode, the recorder will have to fill
the rest of the disc with dummy information to make both L0 and L1 the same size. This process
takes some time, but recorders do not need to record dummy information at the same 1X speed they
use to record broadcast signals. They can record dummy information at a faster speed to shorten
the time it takes to finalize the disc.
The point of transition from L0 to L1 has always caused some difficulties in DVD players. There isoften a slight stutter or “freeze-up” in movie playback at the point where the laser pickup stops,
refocuses, and starts back on the second layer. Skilled authors will put the transition point at ascene-to-scene transition where the change is difficult to detect. For recordable DL DVDs, however,
the transition point is noticeable as a momentary freeze of the picture at best or a complete lock-up
of the picture at worst. Newer DVD players negotiate the transition better than older players. Someolder DVD players simply cannot understand that a “double-layer” and a “recorded” disc can be one
and the same. Clever hobbyists have learned how to deceive these players by using their recording53

7-GB DL DISC

2 ½-Hr. DL DISC

Computer Drive

Home Recorder, SP Setting, VR Format

L1
LO

3.5 GB

3.5 GB

Computers easily divide total file size by two—
half for each layer.

Figure 31

L1
L1

3.5 GBinfo
Dummy

LO

2 hours½ hourHome video recorder keeps recording until theend of the program(s)—then fills the rest of thedisc with dummy information during finalization.

software to change a bit setting in their recording drives that intentionally misidentifies recorded DL
discs as “DVD-ROMs” instead of recorded discs. Although this trick does improve playback
compatibility, it eliminates the chance of multi-session recordings because every phony “DVD-ROM”
disc needs to be finalized in order to appear as a pressed disc. 10
Cost is another drawback for DL discs. Even with two layers, they do not store twice what a single
DVD disc can, yet they cost far more than buying two separate DVD discs. The reason for the costpremium is the difficulty in manufacturing the discs. These discs go through multi-step processes inwhich each applied layer and spacer must be free from trapped air and as clean, flat, and uniform as
possible in order to keep the read or write laser from going out of focus. Manufacturers havestruggled to get yield rates close to half of what they are for regular DVDs.
The manufacturing process for DL discs involves many more steps than that for ordinary DVD+/-R
discs. There are two different methods of manufacturing DL discs in use today: the 2P process andthe inverse stack process (IS). The 2P process is far more common, but it is losing favor because of
unacceptably low yield rates that at best reach 60% and because of some production waste in theprocess.
Figure 32 is diagram of the complicated steps involved in the 2P (Photo Polymerization) process.
The first row of the diagram shows how the first steps are identical to those for regular DVD+R or
DVD-R discs. The main difference is the materials used. The first dye layer is a lower sensitivity dyethat has to be transparent enough to allow laser light to pass through to mark the inner dye layer.
The lower reflective layer also has to allow laser light through it, too, to reach the inner layer. The
second row in the diagram shows the new steps that distinguish 2P manufacturing: a malleable
spacer layer is applied to the first, or outer, layer; and a plastic stamper impresses this spacer withthe wobbled groove for the laser to track during recording. The spacer hardens under the curing
effect of an ultra-violet light (the photo polymerization step for which the 2P process is named). The
stamper is then peeled off the hardened spacer. The next step is coating an inner layer with a highsensitivity dye (L1) on top of the hard spacer. Then a very highly reflective inner layer is applied on
10

Optical discs have Book Type settings recorded onto them by recording drives so that DVD players canrecognize the type of disc when it is inserted into a player. In the early days of the DVD+R, some DVD player
and recorder manufacturers who supported the DVD Forum’s DVD-R/-RW/-RAM formats intentionally set theirequipment up to deny playback of DVD+R/+RW discs. Hackers figured a way to alter the bit settings that thedrive recorded to DVD+R/+RW discs so that instead of appearing as recorded discs, they appeared as regularpressed DVDs with the DVD-ROM Book Type. This method of “cheating” made the DVD+R/+RW discs morecompatible by allowing playback in both the restrictive players as well as the earliest DVD players whose
firmware did not understand the Book Type settings for recordable discs. Changing the Book Type bit settingof DVD+R DL discs from “1110h” to the “0000h” setting for DVD-ROMs allows these media to be played inmany older DVD players whose firmware does not understand how a recordable disc can have two layers..

54

top of the L1 dye layer. The rest of the manufacturing process is similar to that for regular DVDs: therecording half is bonded to the upper dummy blank to complete what is referred to as a DVD9 disc
(Figure 33). The critical steps are assuring that the dye, mirror, and spacer layers are free from any
debris and as flat and uniform as possible with no air bubbles trapped between them
A different method of manufacturing promises to boost yield from 60% to a range of 80-90%. The IS
method (Inverse Stack) makes two separate disc halves in parallel and joins them as a last step.
Although this seems an obvious way to make a two-layer disc, the approach is very different in thatthe upper half of the disc is made in an “inverse” process: the polycarbonate

2P Process—Photo Polymerization

Figure 32

Completed DL Double-Layer Disc

Figure 3355

cover has the metal alloy mirror layer sputtered directly into its molded groove instead of having thephoto-sensitive recording dye coated into it. This arrangement is more like a DVD or CD withaluminum in their grooves than recordable discs, all of which have the dye applied first to thepolycarbonate before a silver alloy mirror layer covers the dye. The metal alloy in the groove
significantly changes the cooling pattern of the disc when heat created by the recording laser istrapped within the groove walls. Engineers must strike a delicate balance in groove geometry,
thickness of the mirror layer, and sensitivity of the dye in order to match the recording characteristics
of discs manufactured in the standard 2P process. The attraction of better manufacturing yields,
however, makes the design effort worthwhile. Figure 34 below compares the structures of DL discs
made with the two different methods.

Figure 34
The fact that a single DL disc costs quite a bit more than two standard DVD+R/-R discs while offering
20% less storage capacity makes a single DL disc less attractive for data storage. Costs will
decrease as yields improve, but the complexity of the design means the cost premium will remain forsome time. Data storage always demands perfect integrity of the files, but the typical jump in errors
at the transition stage in DL discs (Figure 35) suggests caution in storing critical data on such discs.
The laser must stop, refocus, and start again at the very area of the disc that is the most sensitive toany deviation from flatness while it is spinning at the highest rotational speed. Where DL discs makethe most sense is in video recording. Video encoded at the lowest compression rate for the highest
levels of picture quality will only allow one hour of recording on a standard DVD disc. In home video
recorders that means XP recording quality to store a one-hour broadcast or one hour of transferredhome video. SP recording quality will double the amount of playback time with few compromises inquality, but there are compromises nonetheless. DL discs effectively double the amount of recording
time on a single disc without forcing compromises in compression quality except for the split-second56

Figure 35
hiccup at the layer transition. This can be very handy for a number of recording situations:
•
•
•
•
•

two-hour movie broadcasts recorded in the highest quality
movie broadcasts that exceed two hours using SP mode without having to resort to theobjectionable artifacts of LP or SLP modes
sporting events that can exceed two hours
multiple recordings of half-hour or 1-hour programs on a single disc90-minute High Definition video recordings in Windows WMV-HD format (for computer drives
only)

DL drives reached the market long before DL media were ready and available. So far DL discs haveremained expensive and hard to find with questionable benefits for computer users. Home video
recorders are just now incorporating DL capability, and this time it appears the discs were ahead of
their most suitable application. DL discs are meant for video. Although hard drive video recorders
are handy for recording multiple programs, they restrict playback to the recorder itself. DL discs
allow greater flexibility in high quality, high capacity video recording with few restrictions on
portability. Until now, they were a solution ahead of their time.

DVD RECORDABLE SPEEDSThe CD-user who first burns his or her DVD may likely become frustrated at the length of time ittakes to complete a project. CD-Rs hold only audio information or data. DVDs also hold data, seventimes more than a CD-R; but video recordings contain both audio and complex video signals that
require special processing into MPEG formats that a DVD player can recognize. That takes a lot oftime and processing power. One can expect to spend four to five hours of editing, authoring,processing, and recording time for every hour of recorded MPEG-2 video on a DVD recordable disc if
the user is working through a computer. Some software that encodes analogue video into MPEG-2
compressed digital video can take an hour to process a minute. Software developers are aware of
the complexities and have taken steps to simplify and speed up the process, but digital video
recording will always remain more involved than digital audio recording. Those who choose set-top
recorders have an easier time but will lack all the editing and authoring features that can personalize
the final product. The frustration that comes from the length of time involved in such projects mightlead a user to blame the early drives for their slow speeds. The first CD-R recorders worked only at
1X, and the latest drives claim 52X-recording speeds; and the difference is dramatic in recording
times (but it is still a real-time process loading analogue signals into a computer to edit them). DVD57

recording drives are still in their infancy, but they are very sophisticated hardware when one
considers that the pokey CD-R 1X speed was 150 kilobytes per second and recordable DVD 1X is
1.38 megabytes per second—nine times faster. The maximum transfer rate for a standard DVD is
10.08Mbps, 9.8Mbps of which are for video alone. Reducing the transfer rate of data allows longer
recording times on a disc with a fixed capacity of 4.7GB, but the extra time comes at a reduction ofvideo quality. (Recordable DVDs’ 1.38MBps equals 11.08Mbps, a greater transfer rate than that forDVDs because extra data such as synchronization information are also being transferred during
recording.) Recordable drives are already amazingly quick in handling huge amounts of data, anddevelopments in building more powerful lasers now allow DVD recording speeds of 16X. The initiallaser diodes used in DVD recording could produce 70 milliwatts of power and were restricted to a
maximum of 2.4X recording speeds. More powerful 100-milliwatt lasers were used in drives capableof 4X DVD recording, and 250-milliwatt lasers are required for 16X maximum DVD recording speed.
The caution about high-speed recording still remains—always recording at the maximum
speed/maximum laser power shortens the laser diode’s life.
The minimum acceptable laser power in milliwatts is estimated as square root of the recording speed
times 50. A 4X drive requires a laser diode capable of 100 milliwatts; an 8X drive requires aminimum of 140 mW; and the final speed of 16X needs 250 milliwatts. The laser itself requires a 480
MHz clock for accuracy of the timing pulses. At 200 milliwatts the operating temperature of the laser
diode case can reach a temperature of 100° Celsius.
The trick in writing at 16X DVD recording speeds is to devise a write strategy that allows the dye orphase change material to cool enough after one mark/pit is made so that the trailing edge does notaffect the leading edge of the next pit/mark.
There are two ways to reduce this “thermalinterference: 1) increasing the thermal conductivity of the mirror layer to draw off excessive heat(generally by making the metal layer thicker) and 2) thinning the dye layer. Thinning the dye runs therisk of increasing the modulation of the burn marks; so it takes a delicate balance of dye and coating
parameters to optimize the recording characteristics. The precision required to make ideal marks isless than 0.05 micrometers while the disc spins at 180 revolutions per second. That is a linear speedof 56 meters per second-- over 125 mph or 200 km per hour.

Figure 36
Recording speed has an affect only on part of the total time required writing a DVD disc. Finalization
also takes a certain amount of processing time, and it differs for the three different DVD recordable
disc types. Rewritable discs also vary dramatically in the time it takes to erase and format them.
These differences are due to the way in which data are arranged and addressed on the discs. DVD-58

RAM uses molded sectors for address information, and formatting writes the Universal Disc Format
with block information for fast data erasure, storage, and retrieval. See Figure 36.
DVD-R and DVD-RW use molded “pre-pits” in the grooves for address information. Since this format
was originally designed for sequential video recording, data are also added sequentially, as isformatting for the DVD-RW. This means, unfortunately, that formatting and erasing take much longer
time than that for DVD-RAM or for DVD+R and DVD+RW because format information has to be
written over the entire disc. A full erasure can take almost an hour and a half for a DVD-RW insteadof a minute for a DVD+RW disc. New designs in software are being introduced to resolving thisdifference in formatting time, but it will likely always take longer to format and fully erase a DVD-RW
than a DVD+RW. See Figure 37.

Figure 37
DVD+R and DVD+RW use the high frequency 817-kHz signal in their groove as a tool for data
addressing. Instead of a CD-R ATIP, these discs contain an ADIP (ADdress In Pregroove) thatbegins the addressing information in an area of the disc not accessible to DVD players. Unlike themolded sector or pre-pit information that serve as a kind of “postal zip code” for addresses, the highfrequency signal acts as a series of very closely spaced distance markers placed every “50 feet” or
so. New data can be added to old data using the signal as a guide so that the difference inplacement is less than 1 micron. This is the “lossless linking” that avoids the errors that would
appear if the spacing of old and new data were any farther apart. This high-frequency signal method
allows the DVD+RW format to offer some significant features:
•
•

•
•

Erasing files is similar to the “drag-and-drop” method of floppy disks.
o Data writing does not have to be sequential.
o Erasing a file leaves the erased area open for insertion of new data
Formatting a DVD+RW is faster than DVD-RW—just under a minuteo Formatting actually takes longer; but it appears “in the background,” freeing up thecomputer to do other things while formatting continues.
o Older software can take as long as 87 minutes for a DVD-RW but newer software
allows background formatting for DVD-RW, too.
Fully erasing a DVD+RW is faster than DVD-RW.
Finalizing a DVD+RW is faster than DVD-RW--less than a minute after recording.
o Some “finalizing” takes place during recording, similar to background formatting.

59

DVD-RW finalizing time depends on the amount of data—more data on a discactually reduce the time to finalize the disc.
It is easy to edit video files straight to disc on a DVD+RW with Philips’ VR format or Sonic
Solutions’ Open DVD architecture.
o•Figure 38

Comparative Speed of DVD Recordable Drives
FORMAT
DVD-Recordable

SINGLE-SIDE
CAPACITYDATA TRANSFER AT 1X
SPEED (MBps)*

million bytes/s*

4.37 GB

1.321

1.385

CD-R
0.7 GB
0.14590.1536
10*MBps measures in units of 1,024 (2 ) while "millions of bytes per second measures in units of 1,000.

Figure 39
The time spent for the drive to actually record a disc is only 20% or less of the time invested in an
editing/authoring/recording project. What may be more frustrating is discovering that all the time
invested in editing, authoring, processing, and recording a DVD is wasted because it does not play in
any DVD player except the drive in which is was recorded. This is still a stumbling block in this earlystage of the technology. Panasonic introduced set-top players that also play DVD-RAM discs, but inall other cases DVD-RAM’s format for video prevents it from being used in the vast majority ofplayers on the market—or already in people’s homes. DVD+R and DVD-R are physically compatible(that means they have the right dimensions and shape) and are logically compatible (a term thatmeans the DVD-Video format that can be recorded on them is recognized and correct) with DVD
players, and they are much more likely to be successful in the latest players. Some older drives,
however, may not be able to recognize the discs. DVD+RW and DVD-RW have the same problem

60

to a greater degree. Their lower reflectivity might confuse an older DVD player into thinking that they
have a second layer recorded on them so that the player continues to hunt for information that is notthere. Those older players or drives that check format codes may not recognize the code for the
DVD-RW and refuse to play them altogether. Before investing in one format or another based onrecording speed rates or data transfers, one should check to see if the player expected to play therecorded disc can actually recognize it. Compatibility with DVD players and drives is improving all
the time as newer players are developed to handle new media types.

Can DVD Players Play DVD–recordable
discs?
(recorded in the DVD-Video format)
DVD

DVD-R

DVD-RW

DVD-RAM

DVD+R

DVD+RW

Either generalor authoring

1st players*

yes

many

some

no

many

some

2nd generation
players**

yes

most

many

no

most

many

Present
players***

yes

yes

most

no

yes

most

Multi-readplayers

yes

yes

yes

no

yes

yes

Figure 40
1

Of the first players introduced into the market, 95% will play the DVD-R 3.95 GB discs (the first DVD-Rs andthe present authoring DVD-R, but only half are likely to play the 4.7 GB general purpose version DVD-R or the
DVD+R. Few of these players may be able to play the DVD-RW.
2

Almost all of the second generation players will play the 3.95 GB DVD-R discs, and roughly 95% will play the
4.7GB DVD+R and DVD-R discs. DVD+RW and DVD-RW performance improves with the number of playersthat recognize them, but those players are still far fewer than those that successfully play DVD+R and DVD-R.
3

Almost all DVD players sold after November 1999 should play DVD+R and DVD-R discs, and most will also
play DVD+RW and DVD-RW also.

WHICH FORMAT SHOULD I CHOOSE?
The first recordable DVDs tried to match the 4.7-GB capacity of the DVD, but initial limitations
restricted them to 2.6 GB in the case of DVD-RAM and 3.9 GB in the case of the DVD-R. Present
versions of both media have achieved the goal of 4.7 GB, and two-sided discs double that amount to
9.4 GB before formatting. DVD+RW seemed to address most problems very well, but early adopterssoon learned that their DVD+RW recording systems could not record DVD+R discs that followed six
months later. All of these running changes and differences in design and application make therecordable DVD very interesting to those who follow the changes but very confusing to anyone who
needs to choose a format right now. Each format has its strengths and weaknesses, just as
Betamax and VHS did a quarter century ago. The market determined the winner in the video
cassette war, and the market will also decide which format is the most popular for recordable DVD as
well.

61

There is a major difference in this contest of formats from the video cassette format battle. The
choice between VHS or Betamax was a critical one because the recorders and players were thesame devices. Choosing the “wrong” format prevented users from exchanging tapes with anyone
else who had selected the alternate format. Recordable DVD, however, does not force a criticalchoice. The chief issue of compatibility is with DVD players and drives, and both DVD+R/+RW and
DVD-R/-RW appear to be evenly matched in that regard. DVD-RAM’s compatibility is severely
limited because of its protective cartridge; but as far as the “plus camp” and the “dash camp” go,there is no “wrong” choice. The decision should be based on which format offers the user more of
the features he or she needs—and plays on the DVD players and drives one expects to use.
In that regard, there is little practical difference between DVD-R and DVD+R. Both formats arenearly identical in performance. The design of the rewritable DVD-RW was for video applications,
not data. The DVD Forum expected the DVD-RAM to handle data applications. The result is that
DVD-RW’s sequential recording makes formatting, erasing, and rewriting more difficult and timeconsuming. DVD+RW’s design is for both video and data, and it has a distinct advantage in storing
and backing up data. Some drive manufacturers have tried to address the problem by building “dual”
drives that will record both DVD-R/-RW and DVD+R/+RW discs, and the response from the press
and consumers has been enthusiastic. What they may have failed to notice is that the ability torecord both formats means a premium in the cost of the drive simply for an extra processor chip andthe royalties for the additional format. Dual-format drives are an inelegant solution to the format
conflict, but they do eliminate the problem of trying to guess which format to select.

BLUE LASERS—MORE FORMATS, MORE FORMAT BATTLESThe Digital Versatile Disc is a great medium for carrying a lot of data whether those data are used forvideo, super high-fidelity audio, games, information, or any combination of these programs. There
are, however, limitations to the format. As great as 4.7 GB of capacity per side seems, it is notenough for more than twenty minutes or so of high-definition video in the MPEG-2 compression
format. DVD movies look wonderful in comparison to VHS cassette recordings, but they are merely
the best our present TV standards can show. They are not HDTV, and HDTV is the new quality
standard of the future. 11 In order to be capable of carrying high-definition video, DVDs need either
more capacity or greater data compression.
The other limitation is, of course, that there are three competing, incompatible recording formats thatare sometimes not playable on regular DVD players. In order to resolve both limitations at the sametime, DVD developers have proposed a new, future DVD standard for both players and recorders
based on a different laser diode—a blue-violet laser rather than the red lasers used for CDs, CD-Rs,
DVDs, and all three recordable DVDs. The original intent was to have these new players andrecorders able to play today’s DVDs, DVD-Rs, and DVD-RWs in addition to future HD DVD discs andallow a single standard to end the confusion over DVD recording and playback. A single standard
was such a good idea that several other groups proposed their own competing, incompatible “single
standards” to end the confusion even further!
11

In terms of digital photography, high definition video is not so impressive. Standard TV’s 720x480 interlaced
picture resolution is equivalent to 0.3 megapixels. High definition 1280x720p resolution improves to a 0.9
megapixel equivalent, and 1920x1080i is equivalent to two 1.0 megapixel interlaced fields.

62Just as DVDs used smaller pits and more tracks to pack more information on a disc the same size asa CD-R, HD DVD will again shrink the pit sizes and pack more tracks on the same sized disc. The
pits will have to be so small, however, that they will be smaller than the wavelength of a red laser
beam; and the beam will be unable to track the disc. The laser reader/writer will have to use asmaller wavelength of light to read the edges of the pits, and a smaller wavelength means a beam ofa different color.
Light is merely energy that is visible to the human eye. We first begin to see light energy as it passes
from below visibility, the infrared range, to the red range. Hot coals, for example, glow “red-hot” astheir heat increases to visibility. Light energy remains visible through the color spectrum until it
passes beyond violet to the ultra-violet range and beyond. White light is the combination of all thevisible wavelengths together. If white light passes through a prism and bounces off an interior prism
wall, it spreads out according to the wavelengths of the energy components in a “rainbow” effect. Ina real rainbow, sunlight passes through billions of water droplets acting as prisms to divide the light.

Rainbow Colors Spread According to Their Wavelengths:(nanometer=1 billionth of a meter)•Red 780-622 nm•Orange 622-597 nm•Yellow 597-577 nm

GreenInfrared for CD=780nm; ruby-red for DVD= 650 nm

577-492 nm•Blue 492-455 nm•Violet 455-390 nm

Blue-violet laser for DVD HD = 405 nm

Figure 41

Laser Beam Sizes
The higher the frequency of light, thesmaller the wavelength and the beam.

CD beam
780 nmDVD beams
Std DVD
650nm

DVD -R authoring
635 nm

BluBlu-ray/HD DVD
beam
405 nminfrared
ultraviolet

Increasing frequency
Figure 4263Figure 41 shows that the range of wavelengths for each color in the visible spectrum is different.
Red has the widest range and the longest wavelengths. The laser diodes used in CD players and
CD-R/-RW burners are infrared lasers with a wavelength of 780 nm. A different red laser diodeproduces the beam needed for the smaller pit sizes of DVDs. A beam of 650 nm reads DVD
information and a high-power version utilizing 70 milliwatts or more records at the same wavelength
onto DVD-R, DVD-RAM, and DVD-RW discs. DVD-R authoring discs require a 635-nm burning
laser.
In order to decrease pit sizes further to pack more information on a disc, engineers have to movebeyond red lasers. Plans for the new high definition discs are based on blue-violet laser diodes witha wavelength of 405 nm, approaching the ultra-violet range. This wavelength is slightly more thanhalf that of the infrared CD wavelength of 780 nm. See Figures 42 above and 43 below.
Blue-violet lasers are more expensive and difficult to build than red lasers and may have a shorter
lifetime. Manufacturers, however, now feel confident that they can produce enough of them with asignificantly long enough life to make them practical as a replacement for the common red laser
found in CD and DVD players and drives.

Infrared CD laser

Blue-violet DVD laser
405 nm

780 nmFigure 43

CD pit size

CD laser spot of 1.6
microns (μm) from 780nanometer laser. Tracks
are 1.6 μm apart.

Figure 44

HD DVD pit size

DVD laser spot of 1.1 μm
from 650-nanometer laser.
Tracks are 0.74 μm apart.

Blue laser has wavelength of
405 nanometers:
HD DVD spot = 0.62 μm
Tracks = 0.4 μm apart
Blu-ray spot = 0.48 μm
Tracks = 0.32 μm apartCourtesy of Sony and Cinram

64

The first blue laser system on the market is the Blu-ray format. The early Blu-ray versions use thesame MPEG-2 encoding used in today’s DVDs, but the disc is very different from today’s two-piece
DVD sandwich because it uses a single substrate with a very thin recording layer. The substrateitself does not even need to be translucent because the recording and reading lasers do not need topenetrate it. The initial versions of these discs are contained in a cartridge, but that will change intime when scratch-resistant coatings are applied to the bottom recording surface. Other changes tothe format will include more advanced video encode/decode systems than MPEG-2. Specifications
and comparison for the Blu-ray format appear in Figure 45.

Specifications for Blue Laser DVD
HD DVD
Disc thickness:
1.2 mmDisc diameter:
120 mmData capacity:
Single layer-15 GB/side
Double layer-30 GB
Laser wavelength:
405 nmLaser type:blue-violet
Track pitch:
0.4 μWidth of laser spot:
0.62 μMinimum pit length:0.204 μPit width:0.25 μDistance from discsurface to data surface: 0.6 μStandard transfer rate 36Mbits/sec

Blu-ray DVD

DVD

CD

1.2 mm
120 mm

1.2 mm
120 mm

1.2 mm
120 mm25 GB/side
50 GB
405 nmblue-violet
0.32 μ0.48 μ0.15 μ0.25 μ

4.7 GB/side
8.5 GB
650 nmruby-red
0.74 μ1.1 μ0.4 μ0.35 μ0.74 GB
780 nminfrared
1.6 μ
1.6 μ
0.83 μ0.5 μ0.1 μ36Mbits/sec

0.6 μ
11.08Mbits/sec

1.1 μ
1.38Mbits/sec

Figure 45

BLU-RAY
Sony is the first manufacturer to introduce blue laser recorders and media intended for professionaluse. The discs themselves are quite a bit different from DVD recordable discs and DVDs in theirstructure. They are composed of a single polycarbonate substrate instead of two halves. The laser
lens is positioned very closely the disc in a form of “near-field recording.” The numerical aperture* ofthe lens is 0.85 rather than the 0.65 of lenses used in regular DVDs. The complexity of the lensrequired that the first lenses be made of glass rather than the less expensive plastic used for all othertypes of optical recorders and or players, including the competing HD DVD version. (The near-ultraviolet light of blue lasers tends to break down many plastics. Research into durable plastic lenses forblue laser recorders and players continues.) See Figure 46.

65

Figure 46*The numerical aperture is a measure of a lens’s ability to gather or disperse light and its ability toresolve fine detail. The expression of numerical aperture (NA) is a mathematical number derived
from the sine of an angle of light passing through a lens. For example, a lens with a numericalaperture of 0.7 would form a 45° angle from the point of focus at a fixed focal length to the center ofthe lens.

45° angle; sine = 0.71
NA = 0.71

60° angle; sine = 0.87
NA = 0.87

The most distinctive aspect of the Blu-ray is its application of “near-field” recording and playback.
The read/write Blu-Ray laser is much closer to the data surface than it is in CDs, DVDs, or in the HDDVD. The advantage of getting the laser closer to the data is in the reduction of deflection errors if
the medium is not perfectly flat. A non-flat disc will have “tilt” errors toward its outside circumference
that will deflect the reflected laser beam from its intended optical sensor. This tilt error becomes
more critical as pit sizes and laser spots shrink to smaller dimensions in order to pack more data on adisc, and the whole point of moving to blue lasers is to shrink the light wavelengths and pits to thesmallest practical size. The CD-R has a relatively large pit size and laser spot; so a disc’s tilt would
have to be severe to cause a significant deflection error.

66

The DVD, however, packs more data on a disc the same size and thickness as a CD by using asmaller beam size as well as smaller pits and narrower tracks. In order to reduce the effect ofdeflection errors due to tilt of a disc, the data area is moved closer to the laser by sandwiching it
between halves of a disc that are bonded together. The HD DVD uses this same design for its blue
laser disc, and this approach offers HD DVD its greatest advantage: HD DVD discs can use thesame manufacturing equipment as that used for DVDs and recordable DVDs because the disc
design is identical. Manufacturers have gained great experience in making flatter and more uniform
discs as the speed ratings of recordable bonded discs have increased from 2X to 16X. Flatness isessential to keep the recording/reading laser properly focused on at the outermost edge of a pit onetwentieth the size of the finest human hair as the disc spins at a speed of 200kph/125mph. And that
DVD pit is twice as big as the one for HD DVD!

67

The Blu-ray engineers chose to maximize the amount of data to be recorded to a high definition discby making pits and tracks even smaller than those for HD DVD. Over 250 Blu-ray tracks could fit
across the width of a human hair (Fig. 47). The Blu-ray design has taken a “near-field” approach to

Figure 47
recording by bringing a 0.1-micron data surface as close to the read/write laser as possible. This
allows a capacity of 25GB per layer with a minimum amount of tilt deflection error. A secondary
advantage is that the substrate (or “superstrate” at this point) does not need to be of optical grade
polycarbonate because the laser does not pass through it all. Some manufacturers have madeexperimental samples of Blu-ray discs made from recycled paper or other materials that are relatively
durable and can be made uniformly flat. The actual write-once recording layer is a combination ofaluminum/copper alloy and silicon; recording marks are spots where the laser has melted the two toform a light-blocking alloy. Organic dyes are an option for Blu-ray recording.
With every advantage comes some disadvantage, and Blu-ray discs are no exception. Because thedata field is so close to the read/write laser, the surface of the disc has to be kept free as possible
from scratches, damage, and fingerprints. These flaws are less critical for CDs and DVDs because
the laser is focused on the data layer deeper in the disc, and many superficial flaws on the discsurface are simply too out of focus to affect the laser’s ability to resolve the pit edges. The “in-yourface” near-field design of Blu-ray discs has the laser focusing just below the disc surface with little
allowance to ignore surface flaws. A cartridge for Blu-ray was the first solution to the problem, but
consumers prefer discs to be free of such protection (as the DVD-RAM has learned). Manufacturers
now cover the bottom of Blu-ray discs with protective coatings using a combination of micro-silica
particles for hardness and scratch resistance and fluorine-loaded resins that prevent the absorptionof water and oils. The laser lens for Blu-ray near-field recording is more expensive than that forDVDs or HD DVD, especially when it is combined with a red laser for reading CDs and DVDs in
addition to high definition discs. Another disadvantage for Blu-ray is the same as that for any
advanced technology: new production equipment to manufacture a disc quite a bit different fromthose that have preceded it. While HD DVD requires little investment for manufacturing beyond
mastering equipment, Blu-ray requires new production lines in order to produce a disc capable of
25GB per side.

68

Figure 48

HD DVD
Blu-ray is just the first of several different solutions for High Definition video. Toshiba and NEC offer
their own version of a blue-laser DVD that offers a capacity of up to 30GB, enough for three hours of
HD video. Instead of borrowing the MPEG-2 DVD encoding scheme, the Toshiba and NECengineers borrowed the DVD structure and used a newer MPEG-4 encoding scheme for their HD
DVD format. The capacity requirements for HD video in MPEG-2 forced Blu-ray to take extraordinary
steps to maximize the amount of data on a disc. HD DVD, on the other hand, was designed from thestart to use the more efficient MPEG-4 compression and use the less drastic design of today’s DVD
discs, which allows present DVD manufacturing equipment to be modified for production rather thanhave manufacturers invest in all new equipment. A single layer HD DVD version has a capacity of
15GB, and the dual-layer version holds twice that amount. A rewritable version also holds 15GB andthe dual-layer version of the rewritable disc holds as much as 30GB of information. Although the HD
DVD disc has received the approval of the DVD Forum, that approval is for the disc as a DVD video
carrier, not necessarily as a recording medium. The rewritable version of HD DVD will use phasechange alloys similar to those used in DVD rewritable discs, and the write once version will initiallyuse an organic dye. Research continues on other methods, including the aluminum/copper andsilicon recording layers used in Blu-ray discs.

HIGH DEFINITION ALTERNATIVES
A group from Taiwan, the AOSRA (Advanced Optical Storage Research Alliance), is working on
another system physically similar to the Blu-ray disc but differs from it in terms of the encoding, error
correction, and file structure. AOSRA believes there are two advantages for their proposal: 1) theformat is less expensive because it avoids the onerous royalty payments that are beginning toburden optical media and encoding systems, and 2) it offers more than five hours of HD video.

69

High Definition Video Formats
Blu-ray

HD DVD

AOSRA

FVD

Rec. layer:.1 mm thick.6 mm thick.1 mm thick.6 mm thick

Laser:

blue

blue

blue

Red

Wavelength

405 nm405 nm405 nm

650 nm

N/A:

.85

.65

.85

.65

Lens(es):

2

1

2

1

15GB and 30GB
15GB single layer
30GB double layer

17GB and 27GB

6 and 11GB

25GB
Rewritable: 25GB single layer
50GB double layer

Capacity:

Encoding:

MPEG-2 to start;
MPEG-4 AVC; VC-1

MPEG-4 AVC;
MPEG-2; VC-1

AVC (proprietary)

WMV HD

Cartridge:

Only for earliest
versions

no

no

no

Backers:

Hitachi, Matsushita,
Pioneer, Sony,
Philips, Sharp, Dell,
Samsung, Columbia
Pictures, Buena Vista

NEC, Toshiba,
Warner Brothers,
Paramount, NewLine Cinema, HBO,Intel, Microsoft

29 Taiwanesecompanies

29
Taiwanesecompanies

There is a fourth solution called FVD (Forward Versatile Disc) offered by those who either do notwant to have to upgrade all of their mastering facilities to press ever-smaller pits for a more
expensive and, perhaps, shorter-lived laser diode, or who feel that the blue laser has too many
shortcomings. This group uses a different compression scheme from MPEG-2 that can compress
more video data without sacrificing video quality. Advances in algorithms have made suchcompression possible. HD-capable DVD players would retain the red laser diodes but include
different circuitry to identify and decode HD signals while still being able to read today’s DVD discs.
The players would require only a single laser reader instead of both blue and red diodes, and prices
would remain low for consumers. Prices for discs would also remain reasonable because only
software upgrades would be required for the pressing facilities rather than all new mastering and test
equipment and, perhaps, new molding presses. This group also argues that it is too early tointroduce a new format for consumers while standard DVD is still in its growth period and hasreached only half of US household penetration.

LIFETIME EXPECTATIONS OF OPTICAL DISCS
Information is stored on optical discs in order to be saved for later retrieval. How long can thatstorage period last with comfortable assurance that the data can be retrieved? The question is often
asked, “How long will a CD-R or DVD+/-R last?” but what people really want to know is “How long is
my information safe?” There are two parts to that answer: 1) as long as there is equipment that canrecognize the disc and retrieve digital data correctly, and 2) as long as the errors accumulating overtime do not exceed a threshold at which data cannot be retrieved correctly. The first factor is one
that most people forget, but it is likely to be the shorter of the two.

70

Media do not last forever; but at long as they outlast their intended audience they are very useful.
Cave paintings at Chauvet-Pont-D’Arc in France are over 30,000 years old. The Chinese invented
paper about 400 A.D., and this medium is seeing wider use every year despite futuristic claims of
paperless offices. The shellac or vinyl record is a format nearly 120 years old; magnetic tape is 70
years old. Specific formats are showing shorter life cycles as technological developments bringbetter, smaller, and less expensive ways to store information; but the generally accepted lifetime of a
successful consumer format is calculated to be about thirty years—the same as a human generation.
This is no coincidence; consumers do not like to jump from one format to the next and be concerned
about transferring their data and memories from one to the next. They prefer to stick to one
comfortable, familiar format for most of their life and make the leap just once. The younger
generations are the ones who adopt the new formats. The older generations adapt.
Digital media are still relatively new, and the CD itself has only celebrated twenty years of popularity.
The great advantage digital media have is that the information they store can be transferred in thedigital code without apparent loss as long as all the code remains intact. That was not true of
analogue media that transferred their own inherent flaws along with the stored data to anotheranalogue medium with its own inherent flaws. The flaws accumulated, and the quality of the transfer
was inferior to the original. Newer digital formats include methods of accepting transfers from older
formats; and as long as the storage media can last the thirty years of the respective retrieval format’s
lifetime, engineers are happy.
Optical discs, both CDs and DVDs, should easily reach the thirty-year mark and beyond if they are
manufactured well and are stored properly. Contrary to popular belief, these discs do degrade overtime under the effects of heat, humidity, internal chemical reactions, mechanical stresses, UV light,
oxidation, and accumulated scratches. The amount of degradation is measured in the accumulationof errors, and the end of life is defined as the point at which the error rate is so high that data cannot
be reliably retrieved even with error correction. The fewer the initial errors, the longer the life
expectancy can be.
The expected lifetimes can vary for the different types of media and the choices of materials used foreach:• CD-R--Claims have ranged from 50 years to 300 years.
o Organic dyes—cyanine, azo-cyanine, phthalocyanine.
Phthalocyanine shows the best resistance to UV light and to heat, but the other dyes
have seen significant improvements under controlled tests. Dye type is less of afactor in determining life than it was ten years ago.
o Mirror layer—gold or silver alloy
Gold does not tarnish in the presence of sulfur or oxides of sulfur as silver or silver
alloys would; but in a disc with a good lacquer seal, no air or sulfur should reach themetal reflective layer. There are few true gold discs available simply because gold is
so expensive and silver alloys have proved more than sufficient. However, there issome evidence that discs with gold mirror layers have shown superior stability inenvironmental tests than those with typical silver alloys. The fact that silver alloys are
more reflective than gold allows them to reach faster recording speeds than thoseallowed for gold. A uniformly small grain size of the deposited mirror layers should
provide a longer life for the medium.
o Structure
CD-Rs are a single piece of polycarbonate coated with dye and covered with themetal layer and protective lacquer. It is the upper surface that is more susceptible tophysical damage than the bottom of the disc. The CD-Rs have relatively large pit
marks and wide tracks that can still be resolved through moderate scratches on thebottom of the disc.
•

CD-RW—may last as long as CD-Rs. CD-RW discs have the reputation of being
unstable, but factors such as packet-writing complexities and incompatibilities, varying

71laser spot geometries from different drives, and file corruptions are more to blame for thedifficulties than the design or materials of the discs.
o Recording layer—layers of indium-silver-antimony-tellurium
The recording layers are inherently more stable than organic dyes are immune to theeffects of UV light and moderate heat. The alloy crystallizes at 200° C. (420° F.), well
above temperatures that would damage CD-Rs. Chemical changes due to humidity(polycarbonate plastic can absorb water.) can promote ion migration if the disc is notmade well.
o Mirror layer—aluminum alloy
Aluminum is less expensive than silver alloy but has no other advantages or
disadvantages. (Silver is used in CD-Rs because the dyes would corrode aluminum.)A uniformly small grain size of the deposited layers should provide a longer life for the
medium.
o Structure—same as that for CD-R•

DVD+R/-R—claims are up to 100 yearso Organic dyes—azo-cyanine, cyanine, and metal chelate dyes are used for the writeonce versions of DVD discs. These versions of dye have to react quickly to theapplication of the burning laser because the pit marks are very small and the disc
speed is very quick.
o Mirror layer—gold or silver alloy as in the CD-R. Environmental tests indicate that
DVD recordable discs are far more sensitive to humidity than CD-Rs in terms ofincreases in error rates, but it is not clear yet if the humidity is affecting the dye, themirror layer, the adhesive, or the mechanics of the polycarbonate.
o Structure
The fragile recording layer and mirror layer are sandwiched between two halves of a
DVD disc. This offers better protection for these layers than that offered by CD-R and
CD-RW disc. On the other hand, the pit sizes are much smaller and the track pitch ismuch narrower than that of the CD versions; so obstruction from scratches on thebottom of the disc is more likely. The bonding agent between the two halves
introduces more questions about chemical stability. The hub area may or may not bebonded together, and the lack of bonding will mean more care has to be taken wheninserting the discs in a protective case or a locking hub mechanism to prevent
cracking. Tilt, the measure of flatness of a disc, is more critical for DVDs than for
CDs.

•

DVD-RW/+RW/-RAMo Recording layer—layers of indium-silver-antimony-tellurium
These materials are the same as those for CD-RWs but use different formulations.
o Mirror layer—aluminum alloy that is thicker than that for CD-RWs in order to also act
as a thermal conductor.
o Structure—same as that for DVD write-once media.

72

Arrhenius reasoned that the temperature had a direct influence on chemical reactions, and heproposed an equation to determine the effect heat had on activation energy. Eyring’s equation
examines transition states and allows another variable such as humidity:

Arrhenius Equation

Life expectancy

Acceleration
cceleration tests
tests
A

80 70 60℃

25℃

Temperature
ln t1 − ln t 2 =Es  1 1  − k  T1 T2 t = life timeR = relative humidity (%)
k = Boltzmann’s constant  C E 
t = A T d ⋅ exp s  ⋅ exp R  B +  kT 
  T Ln (life time)Ln (life time)E 
t = D0 exp s 
 kT 

Eyring EquationLife
expectancy
Acceleration tests

um

i
id

H
ty

Temperature
E ln(t 50% ) = ln( A) +  s  × T −1 + B × R k 
T= Temperature
Es = activation energy
D, k, A, B, and C = constants(Data courtesy of Imation R&D group.)

Tests conducted on different dyes at differing temperatures produced the graph below (Figure 46).
At a temperature of 25° C. (77° F.), the dyes will remain stable for a period of 30, 50, or 100 years,
depending on the dye being used. The 100-year result is for a typical phthalocyanine dye commonlyused in most of today’s CD-Rs. The calculation is strictly on the heat stability of the dye itself. The
life of the disc also depends on the care in manufacturing and packaging and the quality of the othermaterials used in the disc. Mishandling or exposure to high levels of UV light will have additionaldeleterious effects on life expectancy.
The estimates of life for these media depend chiefly extrapolating the increases in errors on discs
subjected to heat, humidity, and light stability tests. The estimates do not take into account regulardaily use and the damage done by handling the discs on a regular basis. One common estimate ofheat durability is based on a formula developed by Dr. Svante Arrhenius of Sweden in 1889 todetermine activation energy in chemical reactions. Engineers subject discs to different levels of heatfor periods of time and measure the rates of increased errors. Using the “Arrhenius Equation,” theengineers can plot the expected rate of chemical degradation over time to estimate the expected lifeof data on the discs. A second method of estimating expected lifetimes of optical media uses andequation developed by Henry Eyring. Unlike the Arrhenius Equation which uses heat as the stressfactor and a formula based on empirical evidence, the Eyring Equation uses two stress factors—heatand humidity—and a formula based on laws of thermodynamics. This equation may be more usefulfor estimating lifetimes of DVD media because their error rates appear to be much more dependent73

on changes in humidity than those rates for CD-Rs. Under normal conditions, today’s better discs
can easily outlive the format they support as long as the discs are properly made in the first placeand cared for properly. Proper care includes:
1. Keeping discs out of direct sunlight and with limited exposure to light in general.
2. Keeping discs in a cool, dry environment. What is most comfortable for humans is most
comfortable for discs, too.
3. Keeping the discs away from large swings in temperature and humidity.
4. Keeping discs in protective cases when they are not being used.

Life Expectancy for Different Dyes

Li fe Ti me (hrs)

1. E+ 07
100 years
50 years
30 years

1. E+ 0675°C

1. E+ 0585°C
1. E+ 0425°C

1. E+ 03
1. E+ 02
0. 0027

0.00280. 0029

0. 0030

0. 0031

0. 0032

0.00330. 0034-1

1/ T(K )Figure 49

CARE AND HANDLING OF OPTICAL DISCSThe estimated lifetimes of optical discs can only be reached if reasonable care is taken of themduring handling and storage. Most people are familiar with handling these discs, but even a cursory
glance at the bottom of discs in public libraries or from DVD rental stores indicates that the discs are
subjected to far greater abuse than their designers planned. That almost all of these discs still playproperly is a testament to their built-in durability, but accumulated damage will hasten the day thateven good players will refuse to read them.
The most important points in their care and handling are:• Handlingo Hold the discs on the outer edge or through the center hole only to avoid fingerprints
on the bottom of the disc.
o Avoid flexing the discs when removing them from a player or recorder or a storage
case.
Flexing will distort the disc’s flat design and can even damage the innerrecording and mirror layers.
o Do not put excessive pressure on the center hub when inserting the disc in its case.
The center hub area, particularly on DVDs, is fragile. A crack in the hub area can leadto shattering of the disc in a high-speed drive.
o Pick discs straight up from a flat surface; do not slide them.
 Some discs have a special protective coating of extremely fine silicone dioxide
power mixed with the lacquer that offers very good resistance to scratches.

74

•

•

•

Labelingo Use only water-based or alcohol-based pens designed for optical discs.
 The use of other solvents may damage the lacquer surface on CDs and CDR/RW discs.
 The pressure from a ballpoint pen on the surface of a CD or CD-R/RW will
damage the lacquer, mirror, and dye layers and create errors on the disc.
o Paper labels are not recommended for DVD discs.
 The expansion and contraction of moisture in the paper and the accumulationof heat in a DVD drive can alter the flatness of a disc enough that it falls out of
the tilt specification and may not be able to be read. 12
 Paper labels do offer extra protection for the fragile upper surface of a CD-R or
CD-RW.
• Paper CD-R labels must be aligned as precisely as possible to avoid
disc imbalances.
• A disc with a misaligned label should be discarded. Trying to peel thelabel off will likely damage the disc.
• Labeling music discs should not be a problem because they are mostoften read at 1X, but any imbalance may reduce digital audio extraction
speeds.
• Labeling data CD-Rs is not recommended because of the risk ofimbalance-induced errors because CD-ROM discs are generally readat the highest speeds.
Cleaningo Any cleaning should be done radially, that is, from the center hole out to the edge
rather than around the disc. This prevents any accidental scratch from lining up with arecording track. The best solution for cleaning optical discs is a solution designed forsuch discs or the same solution used to clean eyeglasses made from plastic.
o Compressed air used to blow dust off a disc should be used carefully if thetemperature of the air is cold enough to cause a stress fracture.
Storageo Optical discs should be kept in storage cases for protection against contaminants,
light, or accidental scratches.
o Storage cases should stand on their edges so that the disc hangs from its center hub.
o The ideal storage environment should be cool, dry, and dark.
4° C (39° F) < Ideal storage range < 20° C (68° F) at 20-50% relative humidity
Archival: 18° C (65° F) at 35% relative humidity

Memorex has been a well-recognized and trusted supplier of high quality media for many years. We
realize that the consumer will determine which medium or format to choose given enough accurate,honest information to see what fits his or her needs best. Memorex supplies, and will continue tosupply, all the media types available to the market and takes pride in helping to inform the consumer
so that he or she can choose what is best.

12

John Carrier, the inventor of modern air conditioning, developed his first system as a dehumidifier for a printing plant that had trouble
keeping paper in registration when the paper expanded or contracted depending on the humidity in the plant. Keeping the air dry kept the
paper stable as it ran through multiple presses.

75