Talk:CD-ROM

message: The sync pattern for Mode 1 CDs is 0xff00ffffffffffffffff00ff
Is it byte swapped? IMHO this sentance is very confusing. ECMA-130 provides following definition:
 The Sync field shall consist of 12 bytes recorded in byte positions 0 to 11:
 - 1 (00) byte
 - 10 (FF) bytes
 - 1 (00) byte
Besides it's the same for rest data modes too.
And why is this line there at first place? Is it one of 2(!) main consequences extracting RAW data?
Themabus (talk) 14:24, 21 December 2008 (UTC)
thread_title: CD sector contents

message: Why on Earth has no one mentioned the laser wavelength used to read CD-ROMs? I have added it under 'CD-ROM Drives', headed 'Laser and Optics'. Feel free to add more.  —Preceding unsigned comment added by 59.91.241.35 (talk) 19:34, 21 March 2008 (UTC)
thread_title: Optics

message: dics are not hard to find
Entry at http://www.bartleby.com/61/16/C0521600.html , and the discussion is pretty interesting.
----
FYI. Philips Electronics decided already 1972 to spell Optical Discs with a c. This was to differentiate from magnetic disks.
note. the link given above is broken.
Erik Schylander
Kirre46 (talk) 21:12, 10 February 2014 (UTC)
thread_title: Spelling

message: Hello!! When did CDs come out? Some article...
see the compact disk page: 1982 (japan) 1983 (most other developed countries)  —Preceding unsigned comment added by Jasen betts (talk • contribs) 10:01, 20 July 2008 (UTC)
replies: text: I just added the year, I too was bewildered to find a page with so much detail and yet no mention of a date!  CDs were introduced in 1982, CD-ROM in 1985, as far as I can tell. Playclever (talk) 23:25, 18 August 2008 (UTC)
thread_title:  Dates 

message: Hi-Sierra and Joliet are top-tier formats for cd and ISO images. 
Hi-Sierra and Joliet? What are they?
How about the various formats of CD images, ISO, BIN etc? I am aware of these things, but not  there exact meaning, so any informed addtion would be useful. Rich Farmbrough 10:04, 15 Dec 2004 (UTC)
thread_title:  Formats 

message: Is it just a coincidence that the CD was invented with a form factor such that their drives could be the same physical size as those of the earlier 5 1/4 floppy disks?  If not, then this would mean that the inventors of the CD had it in mind all along that they might be used in PCs.  Either way, there should be some discussion of this here and in the main CD article...
--4.245.5.118 23:17, 25 Apr 2005 (UTC)
replies: text: It's just a happy coincidence. According to Kees A. Schouhamer Immink, the size of the CD was chosen based on the cassette tape, i.e. the CD diameter would be about the same as the cassette width. Not because there was any advantage to it, but simply because the cassette was a success. Mirror Vax 08:31, 9 May 2005 (UTC)

text: My understanding was that it was not just that the cassette was a success; it was a success as an in-car format. There was a requirement that it be possible to build CD players that would fit in the same space as a cassette player in a car. Jeh (talk) 09:34, 29 November 2016 (UTC)
thread_title:  Form factor 

message: I am confused. If 100 MB = 95.4 MiB, why is a "700MB" CD-ROM 703.1 MiB? --Byronknoll 05:39, 19 December 2005 (UTC)
replies: text: I added the following text to the Capacity section: "CD capacities are always given in binary units. A "700 MB" CD has a nominal capacity of about 700 MiB. But DVD capacities are given in decimal units. A "4.7 GB" DVD has a nominal capacity of about 4.38 GiB." --Byronknoll 04:19, 30 December 2005 (UTC)
replies: text: This was discussed many times in the CD-R discussion list and also on the CD-R FAQ. Actually CD-R capacity is specified not in binary units, but in time units. The first CD-R's were specified at 74 minutes of capacity, and because there are 75 frames ("sectors" if you will, but that's a different discussion) per second, a 74 minute CD-R has at least 74 x 60 x 75 = 333000 frames. There were small variations depending on the equipment used by the manufacturer (usually there was a bit more space than 333000 frames but the extra space was different between individual discs and brands). When used in mode 1, this gives 333000 x 2048 bytes = 681984000 bytes. Just like with hard disks, manufacturers like to use decimal megabyte to make the discs seem bigger so they printed "680MB" on the packaging. But in binary megabytes this is equivalent to just a little over 650MiB. Jac Goudsmit (talk) 07:14, 29 November 2016 (UTC)

text: For the same reason that a videotape that holds about 243 minutes of material is sold as a "four hour" one. It's easier to say/remember, and means the customer doesn't feel bilked by variations in the manufacturing process. In the early days I had a load of CDRWs of the same, cheap brand for backup purposes... QA set the various batches with permissable write speeds of 2x and 4x, and true capacities between 652~660MiB. But they were all sold as "2x, 650mb". 193.63.174.10 (talk) 14:37, 18 November 2009 (UTC)

text: additional: the people making the labels are both lazy, and pay poor attention to detail - i've seen all manner of sizes listed before - 680mb, 730mb, and others, all on standard 74 and 80min discs... Never mind "MiB" being pretty much something made up by wikipedia and some other people who thought the existing units (developed in an age when computer and SI terminology rarely crossed paths) were too confusing to joe average, and the best way to solve it was to make things even more complex. 77.102.101.220 (talk) 23:35, 31 January 2010 (UTC)
thread_title:  CD-ROM size 

message: I often ask "How are CD-Roms made?" and people invariable answer "They are pressed!" but then cannot elaborate.  Google'd the top a little but could not find much in the way of results.  Can anyone add something to describe the manufacturing process?
They are more like "stamped", because the process happens pretty fast. 66.114.93.6 03:58, 12 January 2007 (UTC)
thread_title:  CD-Rom Mass Production 

message: Regarding this sentence;
:The light/dark and dark/light (pit edge) transitions are translated into 1 bits, the areas with no transitions are translated into 0 bits
Where did this come from? On what level is it supposed to be true? It might apply at the 8-14 encoding level, but it's pretty misleading in that one might read it and reasonably assume that it applied to the file information read off the disk, when in fact there are many layers of encoding between the file information and the bottom (8-14) encoding. Fourohfour 21:01, 4 April 2006 (UTC)
thread_title: 1 and 0 encoding

message: Trollderella 08:13, 14 December 2006 (UTC)
thread_title: When was the first cd rom produced? What about the history of adoption of the format?

message: How is the 1x rate of 150 kilobytes pre second calculated?  Is the unit SI base 1,000 or base 1,024?  —Dispenser 01:18, 19 February 2007 (UTC)
replies: text: If so, the article has many errors in it.  —Preceding unsigned comment added by 71.167.65.179 (talk) 03:17, 14 October 2009 (UTC)

text: To clarify - it's exactly 153,600 mode-2 user bytes per second. 176,400 for audio, 175,200 for mode-1, and 183,750 overall system bytes when you consider the error correction (or mode-1, audio...), subcode, etc. Convert these to your chosen units as you will. 77.102.101.220 (talk) 23:47, 31 January 2010 (UTC)
thread_title:  How is the rate of 150 kB/s calculated? 

message: "Recording data CDs at very high speed (40x) can be done without losing information. However, if done the same with PlayStation or Audio CD it will result in an unreadable PlayStation disc or an audio CD with lots of clicks because there are no error correction codes and the errors are more likely to occur at high speed recording."
After the first sentence, this paragraph from the current article sounds kind of stupid.  It should be deleted or re-written by someone who knows what they are talking about and knows how to write well. -69.87.204.244 14:31, 6 March 2007 (UTC)
thread_title:  recording at high speed 

message: http://en.wikipedia.org/wiki/Floppy_disk
FLOPPY DISKS PAGE TELLS THE YEAR FOR EACH SIZE FLOPPY DISK THAT CAME OUT. WHY NOT CDS?  —Preceding unsigned comment added by 24.188.17.249 (talk) 22:28, 28 September 2007 (UTC)
replies: text: POSSIBLY BECAUSE CDS ONL... ahem, excuse me. Because CDs only come in one main size, and there's probably no clear data on when the 8cm ones (which are essentially just part-recorded 12cm discs, cut down) arrived. By contrast each different type of floppy was basically an entirely new kind of media, from the perspective of formatting, having to have entirely new case designs, and moreover new drives built in order to be able to use them. The difference between a consumer-level 3.5" DSHD 1.4mb floppy and the original 90-ish kb, 8" type made by IBM for its mainframes is immense, and it's only by happy accident you'd ever find a way to read an 8" in a home PC (it can be done, but it's a right bodge and needs particular chipsets, plus a salvaged minicomputer/early micro drive). Whereas the differences between a 210mb 8cm CD, a 12cm one that's merely been burnt to 210mb, or full-up 12cms of 530, 650, 703 and 790mb capacity (63, 74, 80, 90 minute) is trifling and mostly one of trivial set-up detail. Even the difference between a 63 min CD and a DL DVD can be likened to that between a single sided, single/double density drive and a double sided high density one of the same size (5.25 or 3.5")... but in that case, we have release dates for "CD" and "DVD" as discrete classes of 12cm optical disk, and there were no in-between formats such as SSDD/DSDD. The newer drive in both cases will read the disks originally made for the older one, too... The jump from, say, 5.25 inch to 3.5 inch is more like going from CD to Hi-MD. 193.63.174.10 (talk) 15:03, 18 November 2009 (UTC)
thread_title:  CD-ROM SIZE RELEASE DATES 

message: Removed the following from the Bit article, in the "storage" section:
“On storage devices like 1,200,000 nm-thick CD-ROMs, a bit is mechanically etched by intensive laser beam as a pit about 168 nm deep and 670 nm wide of variable length (depending on data type) on concentric tracks spaced 1,600nm apart. The total length of the track in a 650 MB disk thus may span several kilometres. The light of the reading laser is reflected back into the laser, which then picks up that light with a sensor. The transition between a pit and a ground means a 1, and a short period of time on the same level is a 0. No more than 11 consequent zeros may occur, because the laser receives no state change during consequent zeros and has to rely on a timer to know the amount of zeros, whose accuracy is limited. CD-Rs work on the same theory, except that they use dyes instead of pits and ground.CD, CD audio and CD-ROM”
Notice how the numbers differ from those in Compact Disc#Physical details. This stuff here may be of interest.
--Jerome Potts (talk) 04:46, 4 October 2008 (UTC)
thread_title:  technical specs 

message: 15:25, 4 October 2009 (UTC)
replies: text: Weeeelllll you've got a few options. First one, if you can stand the massive inconvenience and cost of not being able to change ANYTHING on your 10-cent disc after making it, is just to put the files onto a vanilla, write-once CDR... nothing short of actually damaging the disc will then be able to alter anything, and said alteration is better described as "destruction". If for some wierd reason this isn't possible you could just try making the file itself have "read only" properties (though this is generally only a minor irritation to human users, who can hit the "are you sure" button or turn the attribute off - it's only really effective against programs) either before or after th burn depending on whether you're doing CDRW/multisession CDR or using a packetCD. More effectively you could look into some digital signature/encryption/etc software that will properly secure the file against unauthorised changes, or even reading/access. This will likely cost you quite a bit more than a few extra throwaway CDRs, however. As a final note, I see you can now buy a drive which has built-in data protection and security features... this might be of interest also. Good luck. 193.63.174.10 (talk) 14:13, 18 November 2009 (UTC)
thread_title:  Untitled text moved from above table of contents 

message: you guys should atlest mention who made it DDDDDDDDDUUUUUUUUUUHHHHHHHHHHHHHHH... IN THE FIRST PARAGRAPH. AND ACTUALLY SAY THE CD ROM WAS CREATED BY.... BECAUSE NOBODY EVER SAYS WHO  —Preceding unsigned comment added by 209.26.59.205 (talk) 16:23, 24 January 2009 (UTC)
replies: text: You guys are awesome, without true genuine winners like yourself, civilization would simply fall apart. I believe there's a personal account somewhere up above from one of the guys on the original Phillips CDROM prototype team? 193.63.174.10 (talk) 15:21, 18 November 2009 (UTC)

text: OK to be more fair to Mahmoud there... looks like you're after the difference between cdrom and cd writer... well... maybe you're having as much difficulty getting hold of an understandable arabic version as I am an english translation of what you said (one significant word remains obscure). So, let's try to put it in simple language. CD ROM = disc is made in a factory, the data is chosen by someone else and cannot be changed. CD writer is a device you use to create your own CDR and CDRW discs. Alright? :) 77.102.101.220 (talk) 00:02, 1 February 2010 (UTC)
thread_title:  DDDUUUUUUHHHHHHHHH 

message: The section on transfer rate is pretty messed up.  I'm not even sure it's self-consistent.  Here is my understanding:  A 1x transfer rate corresponds to a track speed of 1.2 m/s at all positions on the disc, which corresponds to an angular velocity of 500 rpm at the inner diameter and 200 rpm at the outer diameter.  These numbers scale for speeds up to about 12x, I think.  Above 12x, drives typically operate in a constant angular velocity  mode (constant rpm) so that the drive isn't forced to ramp the motor speed up and down as the head seeks to different positions.  In CAV mode, the "x" value refers only to the transfer rate at the outer edge of the disc. At the inner edge the transfer rate is about 2.5 times lower.  Thus, a 52x drive spins at 52x200rpm = 10400rpm.  Period.  Not "up to 26000" as the article now states.  And the track speed at the OD is 52*1.2m/s = 63m/s. Period.  Not "65 to 163 m/s".  I don't have references handy; unless someone gets to it first, I'll at least remove the unreferenced stuff that I know to be wrong.  Spiel496 (talk) 05:02, 21 March 2010 (UTC)
thread_title:  Transfer rate section is in disarray 

message: It would be nice if the 2 different sector formats are described here, incl. why Mode 1 is more common today than Mode 2 Form 1. --RokerHRO (talk) 20:24, 23 January 2012 (UTC)
thread_title:  Mode 2 Form 1/2 is missing 

message: The scope of this article is unclear. It sometimes goes beyond the CD-ROM, properly speaking. In particular, this can be seen in the Transfer rates and Copyright issues sections. The CD-ROM is just one of the CD types discussed in these. These sections discuss all types of data CDs.
It seems we don't have a consistent scope in the article. The scope may be CD-ROM-s everywhere, but in different senses. Sometimes in the strict sense, sometimes in the sense of data CD, read-only or not. It is understandable that this article discusses data CDs, as the CD-ROM was the first form of (general) data CD, but I'm thinking it's probably best to move most discussion on data CDs in general to Compact disc. Otherwise, if we keep using "CD-ROM" in the sense of data CD, we need to make that sense clear in the lead. --Chealer (talk) 15:10, 9 March 2013 (UTC)
thread_title:  Unclear scope / overlap with [[Compact disc]] and other related articles 

message: Should the article mention that early CD-ROM drives for Sun and DEC machines (and maybe other Unix flavour machines) used a 512 byte sector rather than the PC / MSDOS 2048byte sector. This required special versions of the CD-ROM drives (typically with SCSI interface), see:
http://sites.inka.de/pcde/help/dec-cdrom-list.txt
http://www.pimpworks.org/sun/backgrnd.html
John a s (talk) 19:08, 22 April 2014 (UTC)
thread_title:  512 byte sector size for older Sun and DEC machines 

message: Does it specify the byte number of the first byte of the sector, or the mm:ss:ff time code? Does it specify the address at the start of the header of that sector (the first byte of the sync pattern of the header of the sector), or does it specify the address at the start of the data section of the sector, or does it specify the address of the first byte of the address field (in other words, the address field specifies its own address)? Is it a big-endian number, or a little-endian number?  — Preceding unsigned comment added by Benhut1 (talk • contribs) 00:44, 3 May 2014 (UTC)
thread_title:  What format is the address given in? I've got lots of questions on this. 

message: Sorry, but isn't a sector 3234 Bytes? Why can't I find that number on the whole page?  — Preceding unsigned comment added by 93.232.209.201 (talk) 18:08, 16 May 2017 (UTC)
thread_title:  3234 Bytes? 

message: Hello fellow Wikipedians,
I have just modified one external link on CD-ROM. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
*Added archive https://web.archive.org/web/20130126194457/http://sony.storagesupport.com/node/6405 to http://sony.storagesupport.com/node/6405
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
Cheers.—InternetArchiveBot (Report bug) 12:26, 28 July 2017 (UTC)
thread_title:  External links modified 

message: It would be helpful is there was an additional column specifying when drives of the various speeds were made available.  I came to this article looking for exactly this.
I also own both an NEC 3x and 6x speed drives, which aren't represented in the able, at all.  Valgrus Thunderaxe (talk) 01:21, 3 August 2022 (UTC)
thread_title:  Speed Table