A GUIDE FOR LIBRARIANS AND ARCHIVISTS

Care and Handling of 

CDs and DVDs

by Fred R. Byers, October 2003

Council on Library and Information Resources

National Institute of Standards and Technology
Care and Handling of 

CDs and DVDs

A Guide for Librarians and Archivists

by Fred R. Byers

October 2003

Council on Library and Information Resources 

Washington, DC
 

 

 

 

ii

About the Author

Fred R. Byers has been a member of the technical staff in the Convergent Information Systems Division 

of the Information Technology Laboratory at the National Institute of Standards and Technology 

(NIST) for more than six years. He works with the Data Preservation Group on optical disc reliability 

studies; previously, he worked on the localization of defects in optical discs. Mr. Byers’ background 

includes training in electronics, chemical engineering, and computer science. His latest interest is in the 

management of technology: he is currently attending the University of Pennsylvania and expects to 

receive his Executive Master’s in Technology Management (EMTM) degree in 2005.

Council on Library and Information Resources

The Council on Library and Information Resources is an independent, nonprofit organization dedicated 

to improving the management of information for research, teaching, and learning. CLIR works to expand 

access to information, however recorded and preserved, as a public good.

National Institute of Standards and Technology 

Founded in 1901, the National Institute of Standards and Technology is a nonregulatory federal agency 

within the Technology Administration of the U.S. Department of Commerce. Its mission is to develop and 

promote measurement, standards, and technology to enhance productivity, facilitate trade, and improve 

the quality of life. 

The Information Technology Laboratory within the National Institute of Standards and Technology

works with industry, research, and government organizations to make information technology more

usable, secure, scalable, and interoperable than it is today. It develops the tests and test methods that

developers and users of such technology need to objectively measure, compare, and improve their systems.

The Convergent Information Systems Division develops and promotes the exchange, storage, and 

manifestation of digital content via information technology standards, measurements, and technology 

that support the economy, welfare, and defense of the United States. 

ISBN 1-932326-04-9

Copublished by: 

Council on Library and Information Resources

1755 Massachusetts Avenue, NW, Suite 500

Washington, DC 20036

Web site at http://www.clir.org

and

National Institute of Standards and Technology

100 Bureau Drive

Gaithersburg, MD 20899

Web site at http://www.itl.nist.gov

Additional copies are available for $15 per copy. Orders must be placed through CLIR’s Web site.

8

The paper in this publication meets the minimum requirements of the American National Standard for Information 

Sciences—Permanence of Paper for Printed Library Materials ANSI Z39.48-1984.

Copyright 2003 by the Council on Library and Information Resources and National Institute of Standards and Technology. No part 

of this publication may be reproduced or transcribed in any form without permission of the publishers. Requests for reproduction 

should be submitted to the Director of Communications at the Council on Library and Information Resources.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

iii

Contents

Author's Acknowledgments.........................................................................................v

Quick Reference Guide.................................................................................................vi

1. Introduction ............................................................................................................... 1

1.1 Scope of This Guide......................................................................................... 1

1.2 Use of Terms: Information, Content, and Data ........................................... 1

1.3 Comparative Stability of Optical Discs and Other Media ......................... 2

1.4 CDs and DVDs: Operation and Variety ....................................................... 3

2. Ensuring That Your Digital Content Remains Available.................................. 3

3. Disc Structure ............................................................................................................ 5

3.1 Polycarbonate (Plastic) Substrate Layer....................................................... 5

3.2 Data Layer......................................................................................................... 5

3.2.1 Data Layer in ROM Discs ..................................................................... 7

3.2.2 Data Layer in R Discs ............................................................................ 7

3.2.3 Data Layer in RW and RAM discs....................................................... 8

3.3 Metal (Reflective) Layer.................................................................................. 9

3.3.1 Metal Layer in RW, ROM, and RAM Discs ........................................ 9

3.3.2 Metal Layer in R Discs......................................................................... 10

3.3.3 Metal Layers in Double-Layer DVD-ROM Discs ............................ 10

3.4 Lacquer (Metal Protective) Layer (CDs)..................................................... 11

3.5 Optional Surface Layer................................................................................. 12

4. How Long Can You Store CDs and DVDs and Use Them Again?................ 12

4.1 CD-ROM, DVD-ROM Discs......................................................................... 14

4.2 CD-R, DVD-R, DVD+R Discs ...................................................................... 14

4.3 CD-RW, DVD-RW, DVD+RW, DVD-RAM Discs ...................................... 15

5. Conditions That Affect CDs and DVDs............................................................. 16

5.1 Environmental Conditions ........................................................................... 16

5.1.1 Temperature and Relative Humidity ................................................ 16

5.1.2 Light Exposure ..................................................................................... 17

5.1.3 Moisture................................................................................................. 18

5.1.4 Organic Solvents .................................................................................. 18

5.1.5 Magnetism, X-rays, Microwaves, and Radiation ............................ 18

5.1.6 Individual Disc Storage....................................................................... 19

5.2 Surface-Handling Effects .............................................................................. 19

5.2.1 Scratches on the Laser-Reading Side of CDs and DVDs ................ 20

5.2.2 Scratches on the Label Side of CDs ................................................... 20

5.2.3 Scratches on the Label Side of Single-Sided DVDs ......................... 21

5.2.4 Fingerprints, Smudges, Dirt, and Dust............................................. 21

5.2.5 Marking ................................................................................................. 21

5.2.6 Flexing ................................................................................................... 22

5.2.7 Application of Adhesive Labels......................................................... 23

5.2.8 Disc Surface Printing ........................................................................... 24

5.3 Wear from Disc Play...................................................................................... 25

6. Cleaning.................................................................................................................... 25
 

 

 

iv

Appendix 1: Commercially Available CD/DVD Disc Types ................................ 27

Appendix 2: Optical Media Drive Types and How They Handle 

Different Disc Types ............................................................................................. 28

Glossary ........................................................................................................................ 29

Bibliography ................................................................................................................ 38

Tables

Table 1: Disc type, read/record type, data layer, and metal layer.......................... 5

Table 2: Dye type and color appearance—CD-R discs (recordable discs) ............. 8

Table 3: Recommended storage parameters from different sources..................... 16

Figures

Figure 1: User-removable storage-media timeline .................................................... 2

Figures 2, 3: Layers that make up ROM discs............................................................ 7

Figures 4, 5: Layers that make up R discs................................................................... 8

Figures 6, 7: Layers that make up RW and RAM discs ............................................ 9

Figures 8, 9: Two types of double-layer, single-sided DVD-ROM construction .. 10

Figures 10, 11: Two types of double-sided DVD-ROM construction.................... 11

Figure 12: Printable or markable areas of the disc .................................................. 23
 

 

 

v

Author's Acknowledgments

I would like to acknowledge the people who helped make this document 

possible. Contributions came from within the Convergent Information Systems Division at NIST, most notably and with major input from Jian Zheng 

and Richang Lu.

I would like to acknowledge, in particular, Jian Zheng, for his technical 

advice and unending enthusiasm in support of this effort. With his extensive background in optical disc manufacturing and research, he provided 

invaluable insight into the complexities of these discs and issues related to 

their usage.

Other major input from the Division came from Oliver Slattery, Gordon 

Lyon, Joe Navarro, and Dr. Victor McCrary. I would like to give a special 

thanks to Dr. Xiao Tang for suggesting this work and for providing the opportunity to assemble the information in this document, and to Paul Vassallo for his wisdom and guidance.

Others to whom I am deeply indebted for their excellent suggestions 

are: Janet Gertz, director for preservation, Columbia University Libraries; 

Christie Stephenson, director, Digital Conversion Services, University of 

Michigan Library; Melinda Baumann, director, Digital Library Production 

Services, University of Virginia Library; Catherine Murray-Rust, associate 

university librarian, Oregon State University; Samuel S. Brylawski, head, 

Recorded Sound Section, Motion Picture, Broadcasting and Recorded 

Sound Division, Library of Congress; Linda Tadic, director of operations, 

ArtSTOR, The Andrew W. Mellon Foundation; William T. Murphy, president, AVArchives Services; Ed H. Zwaneveld, innovation strategist/coach 

and archival system architect, INNOVAID-E; and Jim Wheeler, Tape Restoration & Archival Services. 

Finally, NIST thanks the Council on Library and Information Resources,

particularly Deanna Marcum, Kathlin Smith, and Amy Friedlander, for 

their patience and constant support from the inception of this project to the 

final distribution of this document. They provided much insight and cooperation on this team effort.

Fred Byers
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

vi

Quick Reference Guide for Care and Handling

Do:

1. Handle discs by the outer edge or the center hole.

2. Use a non-solvent-based felt-tip permanent marker to mark the label side of the disc.

3. Keep dirt or other foreign matter from the disc.

4. Store discs upright (book style) in plastic cases specified for CDs and DVDs.

5. Return discs to storage cases immediately after use.

6. Leave discs in their packaging (or cases) to minimize the effects of environmental changes.

7. Open a recordable disc package only when you are ready to record data on that disc.

8. Store discs in a cool, dry, dark environment in which the air is clean.

9. Remove dirt, foreign material, fingerprints, smudges, and liquids by wiping with a clean cotton fabric in a straight

line from the center of the disc toward the outer edge.

10. Use CD/DVD-cleaning detergent, isopropyl alcohol, or methanol to remove stubborn dirt or material.

11. Check the disc surface before recording.

Do not:

1. Touch the surface of the disc.

2. Bend the disc.

3. Use adhesive labels.

4. Store discs horizontally for a long time (years).

5. Open a recordable optical disc package if you are not ready to record.

6. Expose discs to extreme heat or high humidity.

7. Expose discs to extremely rapid temperature or humidity changes.

8. Expose recordable discs to prolonged sunlight or other sources of ultraviolet light.

9. Write or mark in the data area of the disc (the area the laser “reads”).

10. Clean by wiping in a direction going around the disc.

For CDs especially do not:

1. Scratch the label side of the disc.

2. Use a pen, pencil, or fine-tip marker to write on the disc.

3. Write on the disc with markers that contain solvents.

4. Try to peel off or reposition a label.

General recommendations for long-term storage conditions:

For archiving recordable (R) discs, it is recommended to use discs that have a gold metal reflective layer.

 Archival Storage Facility—Recommendation for storing CDs and DVDs together

Media Temperature Relative Humidity (RH)

CD, DVD Less than 20°C (68°F) 20% to 50% RH

Greater than 4°C (39°F)

A temperature of 18°C and 40% RH would be considered suitable for long-term storage.

A lower temperature and RH is recommended for extended-term storage.
 

 

 

 

 

 

 

 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 1

I. Introduction

1.1 Scope of This Guide

This document describes methods for the care and handling of

optical discs and is intended for use by librarians and archivists in government, academia, and industry. It draws on accumulated industry knowledge and the results of specific studies by the

National Institute of Standards and Technology (NIST).

The document provides guidance on how to maximize the lifetime and usefulness of optical discs, specifically CD and DVD media, 

by minimizing chances of information loss caused by environmental 

influences or physical handling. Discrete topic areas include prevention of premature degradation, prevention of information loss, CD 

and DVD structure, disc life expectancy, and conditions that affect 

optical discs. Other issues relevant to the management or maintenance of optical systems are beyond the scope of this document. 

Excluded, for example, are such topics as care and maintenance of 

the disc drive device and associated hardware and software; digital 

rights and related legal questions; and methods of making, sending, 

and receiving digital copies, including analog-digital conversion procedures. 

This document is intended neither to represent nor imply a standard. It is merely a consensus of several reliable sources on the prudent care of CDs and DVDs.

1.2 Use of Terms: Information, Content, and Data

Information and content as used throughout this document refer to 

audio, video, photographic images, graphics, animations, interactive 

games, computer applications, documents, files or data, and any other digital objects. Data refers to the small pieces of information from 

which “understandable information” is derived. The term is used 

extensively in this guide to refer to the bits recorded in the disc. Such 

bits, or data, are interpreted as ones and zeros by the optical disc 

drive. Eventually, through a series of manipulations by the hardware 

and software of a computer or playback system, these bits become 

“information,” in any of its fully interpreted forms, for the user. 
2 Fred R. Byers

1.3 Comparative Stability of Optical Discs 

and Other Media

Among the digital media, prerecorded and write-once optical discs 

are more stable than digital magnetic tape. Neither optical discs 

nor magnetic tape, however, is as stable as microfilm or paper. With 

proper care, microfilm and non-acidic paper can last for centuries, 

while magnetic tape lasts only a few decades (Van Bogart 1995). Just 

as film types can vary in years of usefulness, one disc type can also 

last longer than another. Temperature and humidity conditions can 

markedly affect the useful life of a disc; extreme environmental factors can render discs useless in as little as a few days.

Media deterioration is but one aspect of the preservation challenge. A potentially more immediate threat is technological obsolescence. Technological advances will no doubt make current optical 

disc types obsolete within several years. If the software currently 

used to interpret the data on optical discs becomes unavailable, a 

migration or emulation technology will be needed to access the data. 

Also, if the current disc-drive technology becomes unavailable, and 

if disc drives produced in the future lack the backward compatibility 

to play today's discs, the information on the discs will likewise be 

inaccessible. Film and paper are much more stable in this regard, as 

human language does not change as rapidly as computer software, 

hardware, or the media format. “Ink on paper,” for example, has 

been used for centuries, and film has not changed significantly over 

the years.

The importance of ensuring that information can be read by 

future generations cannot be overstated. It is vital to have in place a 

preservation strategy that guarantees the sustainability of the collection for as long as possible. The computer-user “industry standard” 

for data storage on removable digital media has changed considerably over the past few decades (TASI 2002). As shown in Figure 1, 

digital media used as recently as 20 years ago are already incompatible with most of today's systems.

Paper Magnetic Magnetic Magnetic Optical Optical Optical ???

(Infrared (Red (Blue/Violet

 Laser) Laser) Laser)

Punch Cassette 5′′ Floppy 3.5” Floppy CD DVD **

Card Tape Disk Disk Disc Disc Disc ???

 Early Late Early Late Near

1970 1980s 1980s 1990s 1990s 2000+ Future Future

** Blu-Ray Disc, Advanced Optical Disc, or other.

Figure 1: User removable storage-media timeline

Timeline illustrates the changes in common “removable” storage media 

(Technical Advisory Service for Images (TASI) 2002, extended by author)
 

 

 

 

 

 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 3

1.4 CDs and DVDs: Operation and Variety

CD is short for compact disc. DVD initially stood for digital video 

disc, then digital versatile disc, but today the term DVD is often used 

without referring to a specific set of words. Both CDs and DVDs are 

optical media, meaning media that use light technology (more specifically, laser light) for data retrieval. A disc drive focuses a laser light 

beam into the CD or DVD to “read” the bits (data) in the disc. The

drive can also “write” bits by focusing the laser beam into recordable

CDs or DVDs. The laser reads and writes data starting from the center

of the disc and proceeding in a spiral direction toward the outer edge.

A pre-groove is stamped in all blank recordable and rewritable CDs

and DVDs to guide the laser as it writes.

Optical discs are differentially identified to designate specific 

features such as recordability, rewritability, and accessibility. For 

example, CD-R, DVD-R, and DVD+R discs are dye-based recordable (write-once) discs—i.e., recordable but not erasable. CD-RW, 

DVD-RW, and DVD+RW discs are phase-change based, recordable, 

(rewritable) discs, or discs that permit the erasing of earlier information and the recording of new material in the same location on the 

disc. DVD-RAM discs are phase-change based, recordable (rewritable) discs formatted for random access, much like a computer hard 

drive. CD-ROM and DVD-ROM discs are pressed and molded, nonrecordable, read-only discs. Brief definitions of the various types of 

optical disks can be found in the glossary; disc structure is covered in 

greater detail in section 3.

2. Ensuring That Your Digital Content Remains Available 

Archivists and librarians place great emphasis on preserving content 

for the long term while ensuring its everyday usability. One of their 

major challenges is to ensure continuing availability of the digital 

content in their collections. Another challenge is to keep the medium 

of storage in a condition as near as possible to the original until the 

content is no longer needed or until it is migrated to a newer technology as the medium becomes outdated. 

Archiving digital content requires an ongoing technological 

strategy to ensure access to stored collections over time (Lee et al. 

2002). Content that has been converted from analog to digital format 

must be migrated to, or made accessible by, newer technologies more 

frequently than is necessary with analog formats. A technological 

strategy for digital content is increasingly important as more analog 

content is converted to digital format and as more content is created 

digitally (born digital). The importance of proper handling of the 

digital media therefore increases as digital collections grow (NDIIPP

2002).

Digital media have become popular, in part, because content can 

be accessed and distributed easily and quickly, and because digital 

media can store the equivalent of reams of documents or hundreds 

of songs on one tape or disc. Optical discs can provide faster access 
 

 

 

 

 

 

4 Fred R. Byers

than magnetic tape to a particular file, song, video clip, document, 

record, or photograph within collections stored on the medium. 

These benefits have prompted significant increases in analog-todigital conversion of existing documents, books, periodicals, photographs, and graphics, as well as music and moving images. CDs and 

DVDs have become popular formats for the recording and storing of 

all types of digital content.

There are, however, potential trade-offs in analog-to-digital conversion. The digital version may not exactly represent the analog original because of the effects of sampling rates, compression algorithms,

or the quality of recording during the conversion. Losses in fidelity

vary in nature and extent, but the possibilities should be considered by

anyone involved in an analog-to-digital conversion process.

Digital copies of digital originals, however, maintain the quality 

of the original, assuming such content has not been altered by system software, hardware, or the condition of the medium. Similarly, 

digital copies of the first digital copy of an analog original will maintain the quality of that copy. Accordingly, continued digital copying 

should not compromise the quality of the content recorded from 

CDs, DVDs, or other digital sources. 

The ability to make copies of equal quality (digital-to-digital) 

means that it is possible—and recommended—to archive one copy 

of a given digital collection (preferably the original) by storing it in 

a location separate from that of frequently accessed copies. Presumably, then, the archived (original) media will be needed only for 

inspection, production of additional copies, or migration to new 

media. One of the most important benefits of archiving is increased 

security; it helps prevent information loss caused by disaster, theft, 

or mishandling. 

If budgetary limits preclude separate locations, then multiple 

copies should be kept at the same location. The original can be designated as “archival,” and the copies “accessible.” If the original is in 

analog format, then the analog version and the original digital copy 

should both be archived. Dual archiving will make both the analog 

original and the digitally converted copy available for future access 

and thus minimize the impacts of deterioration. The version least affected by deterioration will become the version of choice for copying. 

Even where storage facilities do not meet recommended guidelines, 

the original media must be kept isolated and protected, and only 

copies thereof used for everyday access. 

Archived copy—Limited use Frequently accessed copy—Multiple use

• Store in a controlled environment and at a separate 

location, if possible, from the frequently accessed 

copy.

• Store in environmental conditions recommended for 

archival storage.

• Store for easy access.

• Check disc visually for damage or contamination after 

handling.

• Store in environmental conditions similar to usage 

conditions.
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 5

3. Disc Structure

CDs and DVDs consist of the same basic materials and layers but 

are manufactured differently. A DVD is actually like two thin CDs 

glued together. A CD is read from and written to (by laser) on one 

side only; a DVD can be read from or written to on one or both sides, 

depending on how the disc was manufactured. Recordable DVDs 

(DVD-R, DVD-RW, DVD-RAM) can be manufactured with one recording layer on each side. Prerecorded DVDs (DVD-ROM) can be 

manufactured with one or two recorded layers on each side.

3.1 Polycarbonate (Plastic) Substrate Layer

The polycarbonate substrate makes up most of the disc, including 

the area that is read by the laser (opposite the label side on CDs). It 

is present on both sides of a DVD, even a “single-sided” disc with a 

label on one side. This substrate provides the disc depth necessary 

to maintain laser focus on the metal and data layers. It also gives the 

disc enough strength to remain flat. Anything in or on the polycarbonate layer that interferes with the ability of the laser to focus on 

the data layer will result in the misreading of data. Accordingly, fingerprints, smudges, or scratches, as well as such substances as dirt, 

dust, solvents, and excessive moisture (which polycarbonate will 

absorb), can interfere with the ability of the laser to read the data. 

Contact of any foreign material with the polycarbonate substrate 

layer should be avoided.

3.2 Data Layer

As its name implies, the data layer of CDs and DVDs is the layer that 

contains the data. The data appear as marks or pits that either absorb 

light from the laser beam, or transmit the light back to the laser photosensor by way of the metal reflective layer. In CDs, the data and 

metal layers are very close to the top of the disc (label side); in DVDs, 

they are in the middle of the disc (see Figures 1–6). The types of data 

and metal layers used depend on the type of disc—read-only (ROM), 

write-once (R), or rewritable (RW, RAM). Table 1 shows the relationship between the data and metal layers and the disc type.

CD- DVD- Type Data Layer Metal Layer

CD-ROM

Audio/Video

and PC use

DVD-ROM

Video/Audio

and PC use

Read only Molded Aluminum

(also silicon, gold, or silver in 

double layered DVDs)

CD-R DVD-R

DVD+R

Recordable

(Write once only)

Organic dye Gold, silver, or silver alloy

CD-RW DVD-RW

DVD+RW

DVD-RAM

Rewritable

(Write, erase, 

and re-write) 

Phase-changing 

metal alloy film

Aluminum

Table 1: Disc type, read/record type, data layer, and metal layer
6

CD-R, CD-RW

(Single sided)

CD-R/RW are one-sided, 

One recordable layer only

Label, optional

Lacquer

Metal 

Recording/writing layer

Polycarbonate 

Fred R. Byers

Basic Layers of CDs and DVDs

CD-ROM

(Single-sided)

DVD-ROM

(Single-sided)

DVD-ROM

(Single-sided)

DVD-ROM

(Double-sided)

DVD-ROM

(Double-sided)

(All CD-ROMs are 

one-sided)

One recorded layer

(One side)

One recorded layer

(One side)

Two recorded layers

(Both sides)

One recorded layer 

per side

(Both sides)

Two recorded layers 

per side 

Label, optional 

(hub area only)

Polycarbonate

Metal (semi-reflective)

Adhesive 

Metal (fully-reflective)

Center adhesive

Metal (fully-reflective)

Adhesive

Metal (semi-reflective)

Polycarbonate

Label, optional 

(hub area only)

Label, optional 

(hub area only)

Polycarbonate

Metal

Center adhesive

Metal

Polycarbonate

Label, optional 

(hub area only)

Label, optional

Polycarbonate

Metal (fully-reflective)

Center adhesive

Metal (semi-reflective)

Polycarbonate

Label, optional

Polycarbonate

Center adhesive

Metal

Polycarbonate

Label, optional

Lacquer

Metal 

Polycarbonate 

DVD-R, DVD-RW,

DVD+R, DVD+RW, DVD-RAM

(Single sided)

DVD-R, DVD-RW,

DVD+R, DVD+RW, DVD-RAM

(Double sided)

(One side)

One recordable layer only

(Both sides)

One recordable layer per side only

Label, optional (hub area only)

Polycarbonate

Recording/writing layer

Metal

Center adhesive

Metal

Recording/writing layer

Polycarbonate

Label, optional (hub area only)

Label, optional

Polycarbonate

Center adhesive

Metal

Recording/writing layer

Polycarbonate

Basic layers of CD -R/-RW and DVD -R/-RW/+R/+RW/RAM

(Blank recordable discs for all applications listed for ROM discs)

Basic layers of CD-ROM and DVD-ROM

(Replicated discs for audio, video, computer use, or interactive games)
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 7

The dye-based (R discs) and the phase-changing film layers (RW 

discs) both hold data by allowing or blocking light transfer through 

the data layer. The laser-affected (“written”) areas of the data layer 

absorb the “reading” laser beam as it is emitted from the laser to the 

metal layer and reflected back to the laser photosensor. The light 

and dark areas give reflectivity effects that are similar to the interference effect of the “pressed” and molded data in the metal/substrate 

layer in ROM discs. The reflection, whether the result of dye, film, or 

pressed effects, is represented digitally as ones and zeros by the firmware in the disc drive as the laser reads the disc.

3.2.1 Data Layer in ROM Discs

ROM discs are commercially available or made-to-order prerecorded 

discs, also called “replicated” discs. Examples of CD-ROMs include 

the Audio-CD, Video-CD, CD-i, and CD+G, as well as any number 

of CDs used in computer applications. Among DVD-ROMs are the 

DVD-Video, DVD-Audio, and any of various DVDs used in games 

and computer applications. 

The data in CD-ROM or DVD-ROM discs are not actually in a 

separate layer. A molding machine uses a stamper to impress the pits 

(depressions) and lands (surface), which form the data, into the polycarbonate substrate surface. Metal is then sputtered or condensed 

onto the molded substrate to form a “reflective data layer.” The 

reflective metal layer in ROM discs can also be considered the data 

layer because the metal is integrated with the pits and lands in the 

polycarbonate (see Figures 2 and 3). The metal layer in ROM discs is 

usually aluminum. For double-sided DVD-ROM discs, the semi-reflective layer is gold, silver alloy, or silicon.

3.2.2 Data Layer in R Discs 

The recordable, write-once optical disc (CD-R, DVD-R, DVD+R) has 

its data-recording layer sandwiched between the polycarbonate subFigures 2, 3: Layers that make up ROM discs
 

8 Fred R. Byers

strate and the metal layer (see Figures 4 and 5). This layer is an organic dye. The dyes used in CDs and DVDs are the same basic types; 

those used in DVDs, however, are patented by the manufacturer, 

and the disc color does not indicate the type of dye used. The dyes in 

both CDs and DVDs are photosensitive. Bits (marks) are written to 

the dye by a chemical change caused by the laser light beam. This

dye degrades over time, eventually making the disc unreadable. 

The data layer in CD-R discs consists of one of three basic dye 

types, each yielding a different disc color depending on the type 

of dye and the type of reflective metal used in the disc. Even on a 

plain, unlabelled disc, the label side can be a different color from the 

reading side. If the label side of a recordable disc does not have a 

printable surface, a label attached, or some other protective layer, it 

will have the color of the metal used (silver or gold). As for the laser 

reading side, the color will be as indicated in Table 2. 

3.2.3 Data Layer in RW and RAM discs 

The data-recording layer of the rewritable optical disc (CD-RW, 

DVD-RW, DVD+RW, DVD-RAM) also lies between the polycarbonFigures 4, 5: Layers that make up R discs

Dye Type Color appearance

(Viewing the laser reading side of the disc)

Actual Color On Gold Metal On Silver Metal

Phthalocyanine (thalo-sy-a-neen) clear or very light green gold or greenish gold silver

Cyanine (sy-a-neen) blue green blue

Azo (ay-zo) dark blue or deep blue dark green dark blue or deep blue

Table 2: Dye type and color appearance—CD-R discs (recordable discs)
 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 9

ate substrate and the metal reflective layer (see Figures 6 and 7). This 

is a phase-changing metal alloy film. A laser beam writes bits (marks) 

to the film by heating the film above the melting temperature in the 

areas selected for bits. The rapid cooling enabled by the dielectric 

layers on both sides of the phase-changing film causes these bit or 

mark areas to remain in the amorphous state caused by melting. By 

heating the phase-changing film to a specific temperature above the 

crystalline temperature but below the melting temperature, the film 

can revert back to the crystalline state, thereby erasing previous bits. 

The writing and erasing processes can be done together in a single 

pass when rewriting a disc.

3.3 Metal (Reflective) Layer

The metal layer in optical discs reflects the laser beam back to the laser photosensor in the laser head. Three types of reflective metals are 

typically used for this layer: aluminum, gold, and silver or silver alloy. In “double-layer” DVDs, silicon is sometimes used as one of the 

semireflective layers.

3.3.1 Metal Layer in RW, ROM, and RAM Discs

RW, ROM, and RAM discs (CD-RW, CD-ROM, DVD-RW, DVD+RW, 

DVD-ROM, DVD-RAM) use aluminum for the reflective layer, mainly because it is inexpensive and easy to apply. Aluminum oxidizes 

on exposure to oxygen from the environment or to moisture that 

has penetrated the disc. In some earlier CDs, poor sealing allowed 

oxygen to come into contact with the aluminum metal layer, causing 

the aluminum to oxidize. Oxidation of the aluminum diminishes its 

reflectivity, making the disc unreadable by the laser, and is sometimes referred to as disc “rot.” It is the primary cause of ROM disc 

degradation from environmental influences. Not so, however, for 

Figures 6, 7: Layers that make up RW and RAM discs
 

 

 

 

10 Fred R. Byers

RW and RAM disc degradation; the phase-changing film in these 

discs normally degrades at a faster rate than the aluminum in the 

disc oxidizes. 

3.3.2 Metal Layer in R Discs 

In R discs (CD-R, DVD-R, DVD+R), gold, silver, or a silver alloy is 

used for the reflective layer. Silver is slightly more reflective than 

gold but can lose reflectivity with corrosion on exposure to adverse 

environmental conditions. Silver corrodes through reaction with 

sulfur dioxide, an environmental pollutant that can migrate through 

the disc with moisture. Gold is noncorrosive, very stable, and longer 

lasting, but it is also expensive. Either metal should outlast the dye. 

Aluminum is not used with these discs because it can react with the 

dye in the recording (data) layer.

3.3.3 Metal Layers in Double-Layer DVD-ROM Discs

DVD-ROMs can be manufactured with two reflective metal layers 

that allow the laser to read data from both layers using one side of 

the disc. These “double layered” DVDs provide up to four times 

the capacity for content (video, audio, computer applications) as do

“single-layered” DVDs. The laser beam must pass through a semi-reflective metal layer to read data from a fully reflective layer. The outer 

metal layer (silicon, gold, or silver alloy) is semi-reflective; that is, 

it reflects back some of the laser beam and allows some of it to pass 

through to a fully reflective layer (aluminum) and then reflect back. 

Both parts are thus reflected to, and detected by, the photosensor in 

the laser head, which focuses on one layer at a time. 

Figure 8 shows the most common construction for single-sided, 

double-layered DVDs, while Figure 9 shows an alternative construction.

Figures 8, 9: Two types of double-layer, single-sided DVD-ROM construction
 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 11

The difference between these two types is that one (Figure 8) has 

the metal data layers on separate sides (halves) of the disc. In addition to passing through a semireflective metal layer, the laser beam 

must also pass through a special adhesive that binds the two disc 

halves together and does not hinder the laser beam. In the example 

shown as Figure 9, the two metal data layers are on the same half of 

the disc. 

DVD-ROMs can also be double-sided. Figure 10 shows a doublesided DVD that may typically be a DVD-Video providing the video 

in a full-screen TV version on one side of the disc and a wide-screen 

version on the other side. When double-sided DVDs also have double layers on both sides, they may have almost quadruple the capacity of single-sided/single-layered DVDs (Figure 11).

3.4 Lacquer (Metal Protective) Layer (CDs)

A very thin lacquer layer is applied to the label side of CDs to protect the metal from exposure to the environment. (DVDs have no 

such protective lacquer coating.) That layer also gives some limited 

protection from writing on or labeling the disc. However, the CD 

is more sensitive to damage on this side than on the polycarbonate 

side. Since the metal layer is so close to the surface of the label side, 

pointed objects can easily damage the CD by deforming the metal or 

exposing it to the environment. Some solvents can also affect lacquer 

coatings and expose or react with the metal. Once the metal is damaged, the laser cannot read data in the damaged areas. 

Sometimes a manufacturer will add an additional layer designed 

specifically to provide more resistance to fingerprints and scratches 

on the label side of CDs. One particularly effective modification has 

Figures 10, 11: Two types of double-sided DVD-ROM construction
 

 

 

 

 

 

12 Fred R. Byers

been the application of lacquer completely around the edges of the 

disc. In earlier CDs, moisture had been allowed to penetrate to the 

metal through unprotected areas of the disc edge. Clearly, it is as 

important to protect the edges of CDs as it is their surfaces.

3.5 Optional Surface Layer

An optional layer may also be added to a CD or DVD to provide a 

labeling surface (see "Disk Surface Printing," page 24). Such surfaces 

are of four types:

• thermal-printable

• inkjet-printable

• silkscreen-printable

• a surface that will accommodate more than one type of printing 

These layers are applied over the lacquer layer on CDs or over 

the polycarbonate substrate on a single-sided DVD. Some discs 

have an extra coating on which text or logos are printed. In many 

cases, the lettering appears to be stenciled, but it is not part of the 

coating; what one sees is the reflected surface of the metal rather 

than imprinted text or logos. Typically, one can see through this lettered area—and even through the metal—by holding the disc up to 

light.

Because these lettered areas are particularly susceptible to damage, it is most important to avoid writing on or scratching in these 

areas. The only disc surface area that is completely safe from writing or scratching is the clear inner hub or the "mirror band," since 

no data are recorded in these areas. 

4. How Long Can You Store CDs and DVDs and Use Them Again? 

The life expectancy (LE) of optical discs depends on many factors, 

some controllable by the user, others not. 

Factors that affect disc life expectancy include the following:

• type

• manufacturing quality

• condition of the disc before recording

• quality of the disc recording

• handling and maintenance

• environmental conditions

As noted previously, the three basic types of CD and DVD

discs—ROM, R, and RW and RAM—each use a different data layer

material (molded aluminum, organic dye, or phase-changing film,

respectively). Deterioration of this material is the primary cause for

disc degradation and, ultimately, “end of life” for the disc, assuming

proper physical handling.
 

 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 13

Environmental factors can affect the rate of disc degradation. In 

each of the three basic disc types, environmental forces will degrade 

the data layer much faster than the polycarbonate substrate layer 

(the clear plastic that makes up most of the disc). Because degradation of the data layer will render the disc useless well before the 

polycarbonate begins to deteriorate, the relative degradation rate 

for the polycarbonate layer is not used for life expectancy considerations. Physical mishandling of the disc is usually the cause of polycarbonate layer damage. The polycarbonate may also flex or bend if 

stored for a long period of time in a nonvertical position. 

So what is the life expectancy of a disc? First, we must define life 

expectancy. For most users, it means the length of time for which the

disc remains usable. But that implies some acceptable amount of degradation. How much and what type of degradation is acceptable?

With CDs and DVDs, the user does not notice early degradation 

because the error detection and correction capability built into the 

system corrects a certain number of errors. The user notices a problem only when the error correction coding is unable to fully correct 

the errors.

One method for determining end of life for a disc is based on 

the number of errors on a disc before the error correction occurs. The 

chance of disc failure increases with the number of errors, but it is 

impossible to define the number of errors in a disc that will absolutely cause a performance problem (minor or catastrophic) because it 

depends on the number of errors left, after error correction, and their 

distribution within the data. When the number of errors (before error 

correction) on a disc increases to a certain level, the chance of disc 

failure, even if small, can be deemed unacceptable and thus signal 

the disc’s end of life. 

Manufacturers tend to use this premise to estimate media longevity. They test discs by using accelerated aging methodologies 

with controlled extreme temperature and humidity influences over 

a relatively short period of time. However, it is not always clear how 

a manufacturer interprets its measurements for determining a disc’s 

end of life. Among the manufacturers that have done testing, there 

is consensus that, under recommended storage conditions, CD-R, 

DVD-R, and DVD+R discs should have a life expectancy of 100 to 

200 years or more; CD-RW, DVD-RW, DVD+RW, and DVD-RAM 

discs should have a life expectancy of 25 years or more. Little information is available for CD-ROM and DVD-ROM discs (including 

audio and video), resulting in an increased level of uncertainty for 

their life expectancy. Expectations vary from 20 to 100 years for these 

discs.

Few, if any, life expectancy reports for these discs have been published by independent laboratories. An accelerated aging study at 

NIST estimated the life expectancy of one type of DVD-R for authoring disc to be 30 years if stored at 25°C (77°F) and 50% relative humidity. This testing for R discs is in the preliminary stages, and much 

more needs to be done. 
 

 

 

14 Fred R. Byers

4.1 CD-ROM, DVD-ROM Discs (audio, video, inter-

active games, +graphics, computer applications)

CD-ROMs and DVD-ROMs are similar in that they are replicated discs—that is, the data are physically pressed into the disc when it is

manufactured. ROMs are generally mass-produced and contain mu-

sic,video, computer applications, or interactive games.

ROM disc longevity is determined by the extent to which its 

aluminum layer is exposed to oxygen. Oxygen, including pollutants, 

can migrate through the polycarbonate layer or the hard lacquer 

layer (CD label side and edge), carried in by moisture. Oxygen or 

moisture can more easily penetrate through scratches, cracks, or de-

laminated areas in the label. Oxygen can also be trapped inside the 

disc during manufacturing, although manufacturing improvements 

have reduced the likelihood of this. 

If left in a very humid environment, moisture—and oxygen—

will eventually reach the aluminum, causing it to lose its reflectivity. 

The normally shiny aluminum, which resembles silver, becomes 

oxide-dull and much less reflective, like the color of a typical alumi-

num ladder. The combination of high humidity and increased tem-

peratures will accelerate the oxidation rate. 

The life expectancy of a ROM disc therefore depends on the 

environmental conditions to which it is exposed over time. Gener-

ally, it is best to keep ROM discs in a dry, cool environment. If the 

disc is removed from a humid, hot environment to an ideal condi-

tion before damage has been done, it will “dry out” and should be 

as playable as if it had been kept in ideal conditions all along. Other 

contaminates, however, such as inks, solvents, and pollutants, have 

the potential to irreversibly penetrate and to deform, discolor, or cor-

rode the disc, causing permanent reading problems for the laser. 

4.2 CD-R, DVD-R, DVD+R Discs

Most tests of optical disc life expectancy are performed with re-

cordable discs (CD-R, DVD-R, DVD+R). The tests are generally 

performed by manufacturers, and the discs are usually categorized 

by the metal and dye types used in the disc. These discs use gold, 

silver, or a silver alloy for the reflective layer instead of aluminum 

as in ROM discs. Gold will not corrode but is expensive. Silver is 

more reflective and cheaper than gold but is susceptible to corrosion 

if exposed to sulfur dioxide, an air pollutant that can penetrate the 

disc in the same way oxygen can—with moisture. Manufacturers 

use various silver alloys to help inhibit silver corrosion, and most R 

discs available today use a silver alloy reflective layer. The chance 

of silver corrosion from exposure to sulfur dioxide is less than the 

chance of aluminum oxidation caused by high humidity. Nonethe-

less, keeping the disc in a filtered “clean air” environment can mini-

mize or eliminate its exposure to sulfur dioxide. With proper stor-

age, these discs will outlast the technology.

R discs use a dye-based layer (organic dye) for recording data. 

These are “write-once” discs and cannot be erased by CD or DVD 
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 15

drives. The organic dye used in the data layer of R discs degrades 

naturally but slowly over time. High temperatures and humidity will 

accelerate the process. Prolonged exposure to UV light can degrade 

the dye properties and eventually make the data unreadable. Heat 

buildup within the disc, caused by sunlight or close proximity to 

heated light sources, will also accelerate dye degradation. 

Manufacturers claim that CD-R and DVD-R discs have a shelf 

life of 5 to 10 years before recording, but no expiration dates are 

indicated on CD-R, DVD-R, or DVD+R packaging, nor are there 

published reports of tests to verify these claims. Still, it would be 

prudent, in light of these claims, to purchase new discs as they are 

needed rather than to order large quantities and stockpile them for 

future use.

4.3 CD-RW, DVD-RW, DVD+RW, DVD-RAM Discs

RW and RAM discs are generally not considered for long-term or 

archival use, and life expectancy tests are seldom done for this medium. Rewritable discs use a phase-changing metal alloy film for recording data and aluminum for the reflective layer. The alloy film is 

not as stable as the dye used in R discs because the material normally 

degrades at a faster rate; however, these discs should still be stable 

enough to outlast the current CD or DVD technology. 

The phase-changing film is affected primarily by heat, but ultraviolet (UV) light may also be a factor in the aging process. The combination of high temperature and UV light may further accelerate the 

aging process. The combination of high temperatures and high relative humidity will also most likely accelerate the aging process, just 

as it does with the organic dye used in R discs. No lab test results are 

yet available on the effects of these environmental conditions on RW 

or RAM discs. 

The data on the phase-changing metal alloy film layer can be 

erased and rewritten to a limited number of times (about 1,000 times 

for RW discs and about 100,000 times for RAM discs). This rewriting 

does, however, affect disc life expectancy; RW or RAM discs archived 

after the first recording should have a longer life expectancy than 

those that have undergone several erase-recording cycles. Given the 

normal degradation rate alone, the life expectancy for RW and RAM 

discs will be less than that of R discs. Add to that multiple rewrites, 

and the life expectancy can be even less.

Just as the life expectancy of the disc varies with rewriting, so, 

too, does the security of the information itself. Information on RW 

and RAM discs is susceptible to loss or alteration as a result of the 

rewriting. Information on R discs is more secure precisely because it 

cannot be changed or rewritten. 
 

16 Fred R. Byers

5. Conditions That Affect CDs and DVDs

CDs and DVDs can be reliable for many decades with proper handling. As with all other types of media, degradation is inevitable 

over time, but steps can be taken to help prevent it from occurring 

prematurely. This section covers the effects of environmental conditions and physical handling on optical discs.

5.1 Environmental Conditions

5.1.1 Temperature and Relative Humidity

Optical discs will perform well within a wide range of temperature 

and relative humidity conditions. Discs kept in a cooler, less-humid 

environment and not subjected to extreme environmental changes 

should last longer. Optical discs stored in an optimal environment 

will outlast discs that are not. Storage temperature and relative humidity ranges recommended in various technical sources are presented in Table 3.

If stored at a very low temperature relative to the user environment, the disc should be gradually acclimated to the environment in 

which it will be used to reduce stress and moisture condensation. A

Source Media Temperature

Maximum 

Temp. 

Gradient

Relative 

Humidity

(RH)

Maximum 

RH

Gradient

ISO TC 171/SC 

Jan. 2002

CD-R

CD-ROM

+5°C to 20°C

(41°F to 68°F)

4°C /hr

(7°F /hr)

30% to 50% 10% /hr

IT9.25 and ISO 18925

February, 2002

CDs

DVDs

-10°C to 23°C

(14°F to 73°F)

20% to 50% Cycling no 

greater than:

±10%

NARA, FAQ About Optical 

Media, April, 2001

CDs

DVDs

68°F

(20°C)

+/- 1°F /day

(+/- 0.6°C /day)

40% 5% /day

National Archives of Australia, 

April, 1999

CDs 18°C to 20°C

(64°F to 68°F)

45% to 50% 10% /24 hrs

Library Technical Report 

Nov.-Dec. 1997

CDs -10°C to 50°C

(16°F to 122°F)

10% to 90%

DVD Demystified, 

Second Edition, 

Jim Taylor, 2001

DVD-R

DVD-ROM

-20°C to 50°C

(-4°F to 122°F)

15°C /hr

(27°F /hr)

5% to 90% 10% /hr

DVD-RAM -10°C to 50°C

(16°F to 122°F)

10°C /hr

(18°F /hr)

3% to 85% 10% /hr

DVD+RW -10°C to 55°C

(14°F to 131°F)

15°C /hr

(27°F /hr)

3% to 90% 10% /hr

National Library of Canada, 

1996

CDs 15°C to 20°C

(59°F to 68°F)

2°C /24 hrs

(9°F /24 hrs)

25% to 45% 5% /24 hrs

Media Sciences, Inc.

Jerome L. Hartke

July 2001

CD-R 10°C to 15°C

(50°F to 59°F)

20% to 50%

Table 3: Recommended storage parameters from different sources
 

 

 

Care and Handling of CDs and DVDs —A Guide for Librarians and Archivists 17

Direct sunlight to R discs 

is harmful for two reasons:

1. The sunlight’s ultraviolet photons 

(the higher frequency of the sunlight 

spectrum) have enough energy to 

produce a photochemical reaction, 

altering the optical properties of the 

dye (recording layer) molecules.

2. The broad spectrum of unfiltered 

sunlight, infrared to ultraviolet (low 

frequency to high), can impart 

heat to the disc. The increased 

temperature generated by sunlight 

will accelerate the degradation 

or breakdown of the dye layer 

(recording layer) of the disc. The 

combination of high temperature 

and high relative humidity will further 

accelerate that degradation.

significant, abrupt temperature change will cause greater stress than 

a gradual change. Leaving the disc in its packaging will allow gradual acclimation to a changed environment. Discs used frequently 

should be stored at a temperature similar to that of the environment 

in which they are to be used. This minimizes stress from frequent 

temperature changes. 

Given the absence to date of relevant testing, the precise effects of storing CDs and DVDs in freezing temperatures are not yet 

known. Freezing and thawing may create harmful stresses in the disc 

because of differing expansion rates of the layers, but it is unclear 

how much this stress might affect the disc. There may even be a benefit to uninterrupted freezing of a disc for an extended period. Until 

testing is done to measure the effects of freeze-thaw cycles or longterm freezing, the benefits or harmful effects will remain uncertain.

5.1.2 Light Exposure

Effect of Light on ROM Discs

Although the effect of light on ROM discs over time is not known, 

the effects of long-term exposure to light (e.g., UV, infrared, fluorescent) under ambient intensity, such as room lighting, are generally 

thought to be so minimal that light is not considered a factor in the 

lifetime of the ROM disc. Any effect of light on the disc would involve degradation of the polycarbonate substrate (plastic) and would 

become noticeable only after several decades of exposure to daily 

storage facility lighting or sunlight through windows. Degradation 

effects would likely be in the form of “clouding” or “coloring” of the 

polycarbonate. To our knowledge, there is no report on the potential 

impact of this kind of material change on the playability of the disc. 

Light effects on ROM discs, therefore, are considered negligible.

Effect of Light on R Discs

Prolonged exposure to sunlight or other sources of UV light can significantly increase the degradation rate of the dye (recordable) layer 

in R discs. Deterioration of the dye makes it less transparent. As a 

result, some, or all, of the unmarked areas in the dye could be read 

as marks, depending on the severity of degradation. These areas will 

then result in errors when read by the laser.

 The most likely cause of damage to R discs from direct sunlight 

is by heat buildup in the disc affecting the dye. Much of the ultraviolet range of sunlight can be filtered (or absorbed) by glass—e.g., 

the glass of a window. However, the lower light frequency (infrared) 

range will pass through a window and generate heat in the disc. A

disc in a case, or one with a dark label, printing, or color that allows 

it to absorb more sunlight, also makes a disc more prone to heat 

buildup from direct sunlight exposure. The effects of heat buildup 

can be minimized if the disc is kept cool, such as in an air-conditioned room. Exposure to direct sunlight without protection (glass 

or plastic window) will cause the disc dye to degrade more rapidly. 

These observations on the effects of light are based on preliminary 

tests conducted at NIST. 
Light should have minimal, if any, effect on RW and RAM discs, for 

5.1.3 Moisture

18 Fred R. Byers

Effect of Light on CD-RW and DVD-RW, DVD+RW, 

and DVD-RAM Discs

Light should have minimal, if any, effect on RW and RAM discs, for 

the phase-changing film used in such discs is not light sensitive. This the phase-changing fi lm used in such discs is not light sensitive. This 

CD-R, CD-RW, DVD-R, DVD+R, 

DVD-RW. DVD+RW, and DVD-RAM 

discs can become unusable in a 

matter of days. If such a disc is left 

in an environment that allows direct 

sunlight and extreme heat buildup 

(e.g., on the dashboard of a car in 

summertime, or next to a heater 

by a window), the organic dye or 

phase-changing film that holds the 

data will degrade quickly, causing 

the disc to become unreadable. A 

disc is not protected from the effects 

of heat buildup if left in a case that 

is exposed to direct sunlight or 

other sources of heat. Extreme heat 

buildup can also cause warping of 

the disc.

film, however, is affected by heat; in fact, it is heat generated from fi lm, however, is affected by heat; in fact, it is heat generated from 

the intense laser beam that writes data in the phase-changing film. the intense laser beam that writes data in the phase-changing fi lm. 

Heat buildup in RW or RAM discs caused by direct sunlight will 

accelerate the degradation rate of the phase-changing film just as it accelerate the degradation rate of the phase-changing fi lm just as it 

does that of the dye in R discs. The phase-changing film in RW and does that of the dye in R discs. The phase-changing fi lm in RW and 

RAM discs degrades naturally, and from heat buildup by direct sunlight, at a faster rate than the dye in R discs. 

5.1.3 Moisture

The polycarbonate substrate, or the plastic composition, that makes 

up most of the disc is a polymer material that is vulnerable to moisture. Any prolonged exposure to moisture resulting from a spill, 

humid air, or immersion allows water to become absorbed into the 

disc, where it may react with any of the layers. Returning the disc to 

a dry environment will allow the absorbed moisture or water to dissipate out of the disc over time; however, water or a water-based liquid may leave behind, within the disc, contaminants such as dyes or 

other dissolved minerals. If the disc has experienced no permanent 

damage from absorption of the liquid, it should play normally. In 

NIST tests, a CD totally submerged in clean water for 24 hours was 

found to be unreadable initially after removal and surface drying. It 

played normally, however, after 24 hours of drying out at approximately 70°F and 50% relative humidity (normal room conditions). 

5.1.4 Organic Solvents

Contact of the disc with strong organic solvents must be avoided. 

Harsher solvents such as acetone or benzene will dissolve the polycarbonate and thereby damage the disc beyond repair. Limited 

contact (cleaning) with mild solvents such as isopropyl alcohol or 

methanol is permitted, as these solvents evaporate quickly and will 

not dissolve the polycarbonate. They may, however, dissolve or damage labels or optional coatings on the label side of the disc.

5.1.5 Magnetism, X-rays, Microwaves, and Radiation

The effects on optical discs of magnetism, X-rays, microwaves, and 

radiation can be summarized as follows:

• Magnetism should have no affect on CDs or DVDs. 

• X-ray exposure (e.g., from airport detectors) will not harm optical 

discs. 

• Microwaves in a microwave oven will destroy a disc. (It may also 

destroy your microwave oven because of the metal in the disc.)

• Information on the effects of radiation is currently available from 

testing done in connection with the U.S. Postal Service’s irradiation of mail to counter bioterrorism threats. CDs and DVDs have 

been tested at exposure levels of 60 to 300 kilogreys of radiation. 

According to the results, disc data were unaffected by the radia-
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 19

tion; the packaging and discs themselves, however, showed some 

discoloration and had a burnt-substance odor. There were no traces of residual radiation on any of the packages or discs (High-Tech 

Productions, no date). A quantitative summary of these effects is 

also available from Jerome L. Hartke, of Media Sciences, Inc.

5.1.6 Individual Disc Storage

Optical discs should be kept in individual storage containers until 

used and returned to those containers immediately thereafter. Typical storage containers, as listed below, isolate and help protect discs 

from airborne contaminants and other foreign material. They also 

help buffer rapid environmental changes that can cause stresses to 

the disc. Cases are designed to keep surfaces of the disc from contact 

with the inside of the case. Only one disc should be placed on the 

hub (or each hub) in the case. To remove the disc, one should press 

down on the hub tab while holding the outer edge of the disc with 

the fingers and then lift up. Bending the disc while lifting it off the 

hub tab should be avoided.

For long-term disc storage, it may sometimes be prudent to remove the label insert or booklet from inside the case and attach it to 

the outside, perhaps in a sleeve. In theory, the paper can attract moisture and produce higher moisture content in the case. The paper may 

also spread moisture by contact with the disc. This recommendation 

is based on no specific tests of the effects of paper inside a case; it is 

merely a consideration—one that takes on added significance with 

large amounts of paper inside a disc case and higher-than-recommended humidity conditions.

Cases commonly used for individual disc protection include the 

following:

• Jewel case. The jewel case, which comes in different varieties, holds 

one to six discs, depending on its design. It is typically a transparent plastic case with a hinged lid, one or more plastic trays, an 

inlay card for labeling, and an optional booklet. 

• Slimline case. As its name suggests, a slimline case is a slimmer 

version of the jewel case but without the tray. It comes with an inlay card (J-card) and is primarily used for audio discs.

• Amaray case. An amaray case is a plastic case used for commercially available prerecorded (replicated) DVD videos and games.

• Snapper case. An alternative to the amaray case, the snapper case 

is a plastic DVD case with a cardboard cover that is snapped shut 

and held in place by a plastic lip.

5.2 Surface-Handling Effects

Anything on an optical disc surface that impedes the ability of the 

laser to focus on the data layer can result in missing data as the disc 

is being read. Fingerprints, smudges, scratches, dirt, dust, solvents, 

moisture, and any other foreign material can interfere with the ability of the laser to read the data. They can also interfere with the ability of the laser to follow the data track in the disc. Light scratches and 
 

 

20 Fred R. Byers

fingerprints are very common, and while they both can impede laser 

reading, their effects on the disc are somewhat different. Scratches 

affect discs differently depending on the side of the disc affected, the 

severity and direction of the scratch, and the type of disc.

5.2.1 Scratcheson the Laser-Reading Side of CDs and DVDs

Scratches generally cross data lines or tracks on the disc, and how 

bad (deep and wide) they are will determine the extent of interfer-

ence with laser focus on the data. Small or occasional scratches will 

likely have little or no effect on the ability of the laser to read the 

disc, because the data are far enough below the surface of the disc 

that the laser is focused beyond the scratch. This is comparable to the 

effect of a light scratch on a pair of eyeglasses; it does not markedly 

impair vision because the viewer’s eyes are focused beyond it. 

Even assuming a scratch is deep or wide enough to influence la-

ser focus, error detection and correction coding in the disc drive can 

in many cases recover the misread data. However, scratches that are 

deep, wide, or bunched together can adversely affect the readability 

of the disc. These scratches can cause the laser to misread enough 

data to make error correction coding ineffectual. 

Whiledata errors generated from scratches that run outward from

the center of the disc stand a good chance of correction by the error 

correction firmware, scratches running in the direction of the track, 

the same direction as the laser reads the disc, are more likely to cause 

uncorrectable errors. These uncorrectable errors are called E32 in the 

Red Book for CD specifications, and PO Error in DVD specifications.

 If scratches are deep enough to damage the data or metal layers 

on the reading side of a disc, the data cannot be read or repaired.

5.2.2 Scratches on the Label Side of CDs 

Scratches on the label side of CDs can be a more serious problem. 

Because the reflective metal layer and data layer are so close to the 

surface of the label side of the disc, they can be damaged very easily. 

A slight indentation, or pinhole in the metal from a scratch, pen, pen-

cil, ultrafine marker, or other sharp object will destroy the reflectivity 

of the metal in that area on the other side (laser reading side) and the 

readability of the data by the laser. This type of damage cannot be 

repaired.

As with scratches on the laser-reading side, optical disc drives 

are usually able to read through minor damage easily, even if the 

damage is caused from the label side. The difference is that this 

damage is permanent. If the error detection and correction firmware 

in the disc drive cannot correct the data, it will not be recoverable. 

Scratches that do not reach through the thin protective lacquer coat-

ing should have no immediate effect but may ultimately expose the 

metal to moisture, air pollutants, or other adverse environmental 

influences. 

Adhesive labels (see page 23), though also somewhat vulnerable 

to adverse environmental influences, can provide CDs with extra 

protection from scratches. The extra layer on printable discs likewise 

offers protection. 
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 21

5.2.3 Scratches on the Label Side of Single-Sided DVDs 

Scratches on the label side of single-sided DVDs are not likely to 

pose a problem. The metal layer so prone to damage in CDs is in the 

middle of DVDs. Its location makes this layer almost impervious to 

surface scratches; it is in fact unlikely to be affected by any but the 

deepest scratches—those deep enough to reach the center of the disc 

where the metal and data lie. 

5.2.4 Fingerprints, Smudges, Dirt, and Dust

Fingerprints, smudges, dirt, or dust on the laser reading side of the 

disc can disrupt laser focus on the data even more than a scratch can. 

Dirt or dust on the disc will block or reduce the light intensity of the 

laser. If severe enough, it will cause the disc drive to miss data as the 

disc is being read. Fingerprints, smudges, or dirt cover wide areas of 

data and will cause the laser beam to go out of focus or lose intensity. 

They will also cause widespread misreading of data along the data 

lines or tracks, to an extent that exceeds the error correction capability of the disc drive. Dust can also spin off into the disc drive and 

collect on the laser head or other internal components. Fingerprints, 

smudges, and dirt are easier to remove than scratches; it is simply a 

matter of cleaning them off. 

To summarize, the effects of scratches versus fingerprints and 

smudges on the laser reading side of a disc include the following:

• Occasional fine scratches will typically not affect the focus of the 

laser.

• Deep scratches can affect the focus of the laser and cause errors.

• The error detection and correction coding system in the disc drive 

will correct many errors caused by scratches.

• Fingerprints and smudges can cause more errors than scratches 

and are more likely to overwhelm the error correction coding system capability.

• Scratches in the direction of the track (tangential direction) are 

worse than those going from the center of the disc outward (radial 

direction). 

• Like fingerprints and smudges, several scratches close together 

can also overwhelm the error correction coding system capability.

5.2.5 Marking

Marking and labeling a CD or DVD is an essential process in its creation. CDs and DVDs, or their containers, are labeled in some form 

or fashion so that they can be identified and organized. When labeling a CD with markers, the composition of the ink in the marker and 

the style or design of the marker should be considered.

The inks in markers vary in chemical composition and are 

formed from pigments or dyes, and solvents. Inks are divided into 

three basic categories according to the type of solvent used: waterbased, alcohol-based, and aromatic solvent-based. Within these categories, inks are further divided according to their permanence and 

their application to different surfaces.

Markers themselves also vary in form: there are fine-point, extra 
22 Fred R. Byers

Never use a fine point or rolling ball 

marker on a CD because it may 

scratch or depress the surface of 

the disc and permanently damage 

the metal and data layers.

fine-point, rolling-ball, ballpoint, soft felt-tip, and chisel-tip. Some 

are ideal for CD labeling; others can cause damage. 

Numerous CD vendors have noted that the thin protective 

lacquer coating can deteriorate from contact with certain solvents 

in markers. To eliminate the risk, water-based markers are recommended for CD labeling. As a solvent, alcohol is generally less 

damaging than xylene and toluene, which are common in aromatic 

solvent-based markers. According to anecdotal reports, alcoholbased markers can be used to label CDs without causing performance problems. However, there are no explicit lab test results 

to show what effect solvents in markers have on different CDs or 

DVDs, particularly over the long term. 

The vulnerability of the metal in CDs, because of its proximity 

to the surface, should be considered when choosing a marker. The 

metal is particularly susceptible to damage from scratches, scrapes, 

or denting caused by surface marking. A felt tip marker will minimize the risk of scratching or denting. 

As mentioned before, CDs and DVDs look similar, but their 

layer structures differ. The recording layer of a CD is located just 

beneath the labeling side. On a DVD, the recording layer is in the 

center of the disc. In theory, solvents from a solvent-based marker 

will not penetrate to the center of a DVD through the polycarbonate layer on both sides of the disc. Consequently, the data and metal layers in the center, in theory, should not come in contact with 

any harmful solvents. Nevertheless, the same precautions taken in 

labeling CDs are advisable for DVDs. The marker used to label a 

CD will work just as well on a DVD. Restricting oneself to the CDsafe marker will also eliminate the potential for mix-ups in the use 

of distinctive CD or DVD markers.

Many vendors sell CD-safe markers, and they vary in ink solution. They should not contain any solvents harmful to CDs or 

DVDs but should have a permanent quality. For risk-free labeling 

of any disc, it is best to mark the clear inner hub or the so-called 

mirror band of the disc, where there are no data (see Figure 12). 

5.2.6 Flexing

Flexing (bending) the disc by any means, such as removing it from 

a jewel case or sitting on it, may harm the disc by causing stresses. 

The disc should be stored in its case and placed vertically, like a 

book, on a shelf. Long-term horizontal storage, particularly in a 

heated environment, can cause the disc to become permanently 

bowed. While the data may still be intact, the disc may not operate 

properly in the drive or permit the laser to follow the track. The 

maximum degree of flex (bend) or number of times a disc can be 

flexed before it incurs damage is not known. To minimize the risk 

of damage, it is better to avoid flexing discs.
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 23

5.2.7 Application of Adhesive Labels

Adhesive labels should not be applied to optical discs destined for 

long-term storage (more than five years). The label could delaminate 

over time and interfere with disc drive operation. The adhesive in 

some earlier labels has also been known to react with the lacquer 

surface. Any attempts to peel the label off could cause damage to the 

lacquer and metal layers in CDs. DVDs are different; peeling a label 

off a DVD would not have the same adverse affect because the metal 

layer is not near the surface. Still, removing a label, or any portion 

thereof, from the surface of a disc can cause an imbalance in the spin 

of the disc in the disc drive, making the disc unreadable. DVDs are 

more susceptible to reading problems from minor imbalances than 

are CDs. To ensure the long-term availability of information on a 

disc that already has an adhesive label, the information on the disc 

should be copied to, and stored on, a disc without such a label.

Adhesive labels may be well suited for short-term disc usage 

(less than five years), and can even add a layer of protection from 

scratches and other potentially harmful contact. On the other hand, 

such labels are vulnerable to adverse environmental conditions: they 

can dry out or absorb moisture, and they can be affected by heat or 

cold even more than the disc itself. Such conditions may cause the 

label to delaminate. Disc manufacturers advise against using adhesive labels because they can create unbalanced disc spin, resulting in 

premature wear of the drive. If a label is used, it should be manufactured for use on CDs or DVDs, and an appropriate disc label applicator tool should be used to affix the label. The label applicator tool 

should center the label on the disc so as to maintain the disc balance 

as much as possible. 

Figure 12. Printable or markable areas of the disc
24 Fred R. Byers

5.2.8 Disc Surface Printing

Printing labels directly on CD-R and DVD-R requires the use of discs 

to which a printable surface is added at time of manufacture. The fol-

lowing printing information relates mostly to CD-R discs, but would 

also apply to the DVD-R versions.

Inkjet printing and thermal transfer printing are commonly used 

for labeling the surfaces of CD-R discs. Each involves a different 

technology to place inks on the printing surface of the disc; few ink-

jet-printable and thermal printable CD-Rs are interchangeable. 

The printable area on a DVD disc depends on whether the disc 

is single- or double-sided. A label may be printed on the top side of 

a single-sided DVD, much like on a CD. However, the performance 

of a DVD is more sensitive than that of a CD to any imbalance of 

the disk. Because ink affects the flatness and balance of a disc, full 

surface printing may not be the best choice since the ink may not 

be uniformly distributed over the disc surface. Nonetheless, if you 

choose to print labels on your discs, full surface printing is better 

than partial surface printing. For full surface printing of either a CD 

or a DVD, a white, printable base coat is available.

“Pit art” labeling, as an alternative to printing, avoids the flat-

ness and balance issues. The pits are produced on the label side 

(without having a printable surface), creating a mirrored, holographlike pattern on the metal layer that becomes the label. Because no ink 

is used, the flatness and balance of the disc are not compromised. 

If a DVD disc has data on both sides (double-sided), neither 

printing nor pit art may be used in the data area of the disc. Only the 

area of the mirror band and the area between the mirror band and 

center hole may be printed on or marked.

Thermal Printing

In thermal transfer printers, a print head that contains resistive ele-

ments in a linear array heats ink-coated films (ribbons). The head is 

in direct contact with the uncoated side of the ribbon, and the inkcoated side of the ribbon is in direct contact with the disc’s printable 

surface. The ink is heated, causing it to melt and adhere to the print-

ing surface. Specially formulated materials are used for the printable 

surface of the disc to enhance ink transfer efficiency and adhesion. 

Only specially designed thermal printers—not thermal printers de-

signed to print on paper—can be used to print directly on the surface 

of thermal printable CD-R discs.

Inkjet Printing

In inkjet printers, inks are sprayed, via droplets of an ink solution, 

onto a specially designed printable surface material on the disc. This 

surface is designed to hold the ink droplets in place while absorbing 

the liquid components of the ink. 
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 25

Silkscreening

Silk screening on CDs or DVDs uses a UV-curable ink to keep the ink 

colors from running together. That ink cannot contain any chemically 

active components that can affect the disc after the curing process or 

abrasive particles in the ink pigments that can damage the protective 

layer of CDs. 

5.3 Wear from Disc Play

CDs and DVDs do not wear from friction as vinyl records or tapes 

do. There is no physical contact with the disc in the area that the laser uses. 

ROM Discs: The laser light will have no effect on the data or 

metal layer in ROM discs. In theory, it is possible for the disc to be 

read so many times that the cumulative effect of the laser light can 

eventually affect the polycarbonate. There is, however, no record of 

such discs having been played a sufficient number of times to incur 

damage from laser light. Accordingly, it is felt that any effects of the 

light on ROM discs is negligible. It is assumed, in fact, that the disc 

would likely fail much earlier from some other condition than from 

the effects of laser light. 

R discs: In theory, R discs should have a limited number of read 

times (several thousand) because of the cumulative effect on the data 

layer from the laser light. As with ROM discs, the polycarbonate may 

also eventually be affected, but there is no recorded evidence of ill 

effects of laser light, so such effects are deemed negligible.

RW discs: RW discs, unlike the other types, can “wear-out.” CDRW and DVD-RW discs should last for about 1,000 rewrites, and 

DVD-RAM discs, 100,000 times, before the rewriting capability is 

lost. The reading functionality of the disc should continue for a limited number of read times after each writing. While the maximum 

number of read times possible after writing is unknown, it may become fewer after each successive writing. 

6. Cleaning

CDs or DVDs do not require routine cleaning. It is best to clean the 

disc only when it is absolutely necessary, specifically:

• before storing, when surface contamination is visible

• before recording, when surface contamination is visible

• before playing, to prevent surface contamination from being 

“flung off” while the disc is spinning in the disc drive

• when readability (playability) is impaired and surface contamination is visible

In general, avoid using organic solvents. Harsher solvents (acetone, benzene) will dissolve the polycarbonate and damage the disc 

beyond repair. Mild solvents (isopropyl alcohol, methanol), however, 

may be used. These mild solvents evaporate quickly and will not dis-
26 Fred R. Byers

solve the polycarbonate. 

Other solutions that are not harmful are water-based lens clean-

ers or water-based detergents (with mild soap) formulated for clean-

ing CDs or DVDs.

The polycarbonate substrate is a relatively soft and transparent 

type of plastic. Each time a disc is wiped, rubbed, treated with some 

solution, or otherwise manipulated for cleaning, that substrate, and 

thus the disc itself, is at risk of scratching or contamination. 

If the disc needs cleaning, remember these tips:

• Use an air puffer to blow off dust. • Use a soft cotton cloth or chamois to wipe the disc. • Try cleaning with a dry cloth first, before using any cleaning 

solutions.

• Do not wipe in a direction going around the disc. • Wipe from the center of the disc straight toward the outer edge. • Avoid using paper products, including lens paper, to wipe the 

disc.

• Avoid using anything abrasive on the surface of the disc. • If the disc has a heavy accumulation of dirt, try rinsing it with wa

-

ter first.

• Use commercially available water-based detergent formulated for 

cleaning the surface of optical discs.

• Use isopropyl alcohol or methanol, as an alternate to water-based 

detergents, to clean the disc surface. 
 

 

 

 

 

 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 27

APPENDIX 1: COMMERCIALLY AVAILABLE CD/DVD DISC TYPES

CD

CDs are single-sided (One recorded layer or recordable layer on one side of the disc)

Disc Type

Storage

Capacity

Typical 

Uses

CD-ROM, Audio-CD, Video-CD Read only 650MB Commercially available:

computer programs, music

CD-R Record once 650MB User recording 

music, computer data, files, applications CD-R Record once 700MB

CD-RW Rewritable 650MB User recording

computer data, files, applications CD-RW Rewritable 700MB

DVD

• DVD-ROM, DVD-Video (commercially available pre-recorded DVDs), can be single- or double-sided with one or two data 

layers on one or both sides of the disc (a maximum total of four data layers).

• DVD-R, DVD+R, DVD-RW, DVD+RW, are only available as single-sided, single-layer (SS/SL).

• DVD-RAM is available in double-sided, single-layer (DS/SL).

Disc Type

Storage

Capacity

Typical

Uses

DVD-ROM, DVD-Video, DVD-Audio Commercially available:

Movies 

Interactive games

Programs 

Applications

Single side has one data layer (SS/SL) Read only 4.7GB

Single side has two data layers (SS/DL) Read only 8.54GB

Both sides have one data layer (DS/SL) Read only 9.4GB

Both sides have two data layers (DS/DL) Read only 17.08GB

DVD-R (General) Record once 4.7GB General use:

One time video recording and data 

archiving

DVD-R (Authoring) Record once 3.95GB 

or 4.7GB

Professional use:

Video recording and editing

DVD+R Record once 4.7GB General use:

One time video recording and data 

archiving

DVD-RW Rewritable 4.7GB General use:

Video recording and PC back-up

DVD+RW Rewritable 4.7GB General use:

Video recording and editing, data 

storage, PC back-up

DVD-RAM Computer data: 

Storage repository for updateable 

computer data, back-ups Single-sided Rewritable 2.6GB 

or 4.7GB

Double-sided Rewritable 5.2GB 

or 9.4GB
 

28 Fred R. Byers

APPENDIX 2: OPTICAL MEDIA DRIVE TYPES 

AND HOW THEY HANDLE DIFFERENT DISC TYPES

DVD drive types and what they can do with each disc type

Disc Type

DVD ROM 

Play only 

(computer)

DVD-R

(General)

Records 

General -R

DVD-R

(Authoring)

Records 

Authoring -R

DVD-RW

Records

-RW, General -R

DVD-RAM

Records RAM

DVD+R/+RW

Records 

+R, +RW

Read Write Read Write Read Write Read Write Read Write Read Write

DVD-ROM Yes No Yes No Yes No Yes No Yes No Yes No

DVD-R (General) U No Yes Yes Yes No Yes Yes Yes No Yes No

DVD-R (Authoring) U No Yes No Yes Yes Yes No Yes No Yes No

DVD-RW U No Yes No Yes No Yes Yes U No U No

DVD-RAM R No No No No No No No Yes Yes No No

DVD+R U No U No U No U No U No Yes Yes

DVD+RW U No U No U No U No U No Yes Yes

CD-ROM Yes No Yes No No No Yes No U No Yes No

CD-R Yes No Yes Yes No No Yes Yes U No Yes Yes

CD-RW Yes No Yes No No No Yes Yes U No Yes Yes

 U = Usually R = Rarely

DVD-Video

DVD-Audio

All DVD drives should play DVD-Video or DVD-Audio if the computer has DVD-Video or DVD-Audio player software installed.

DVD-RAM drives are questionable.

* Most computer DVD drives are backward compatible to CDs, meaning they can read or read/write CDs.

* Some drives are the combination of more than one drive type, providing compatibility with different DVD and CD disc types.

CD drive types and what they can do with each disc type 

Disc Type

CD ROM

Play only

CD-RW or CD-R/RW

Records -RW, -R

CD-R

Records -R

Read Write Read Write Read Write

CD-ROM Yes No Yes No Yes No

CD-R Yes No Yes Yes Yes Yes

CD-RW Yes No Yes Yes No No

DVD-Video, Audio

DVD-ROM

DVD-R (General)

DVD-R (Authoring)

DVD-RW

DVD-RAM

DVD+R

DVD+RW

DVDs do not work in CD drives or CD players. 

Home DVD video player compatibility with each disc type

Disc Type DVD Video Player Comment

DVD-Video

DVD-Audio Plays - DVD-Video and DVD-Audio are a type of DVD-ROM commonly used in home 

DVD-Video or DVD-Audio players.

- Use of the term DVD-ROM, typically refers to replicated (commercially available 

pre-recorded) DVD-ROMs for computer applications.

DVD-ROM

DVD-RAM

N/A

DVD-R (General)

DVD-R (Authoring) Depends If the disc is formatted correctly, it should play in newer home DVD video players.

DVD-RW, DVD+R, DVD+RW

CD-ROM (Video-CD) Depends

If the CD-ROM, CD-R, or CD-RW are formatted as V-CD, (Video-CD), some DVD 

video players will play them (some DVD players compatible with MPEG 1).

CD-ROM (Audio-CD) Plays

CD-R (V-CD or audio formatted)

CD-RW (V-CD or audio Usually

formatted)
 

Glossary

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 29

analog (content and storage media): 

• analog content: content that uses a mechanism in which data are 

represented by continuously variable physical quantities (e.g., frequency and amplitude of sound recorded on tape, image printed 

on film).

• analog storage media: stores analog content (e.g., paper, photographic paper or negative, film, microfilm, audio tape, VHS tape, 

vinyl records, stone, cave wall). 

To be used in computers, analog content must first be converted into 

a binary code. Such content that has been converted is often referred 

to as digitized. Digitizing is the “sampling” of an analog signal or 

content at predetermined interval locations; the signals are then converted into binary (1,0) form (digital). The closer the intervals, the 

more closely the digital signal represents the analog signal. 

amaray case: 

A plastic case normally used for commercially available prerecorded 

DVD videos and games.

archivist:

A person in charge of archives administration, including preservation.

archive:

(noun) A place where materials are preserved.

(verb) To file, collect, or store materials or media in an archive, or archive collection, for preservation.

audio CD, also, CD-DA (CD-Digital Audio), CD-A (CD-Audio):

A format that holds about 60 minutes of audio data, in up to 99 

tracks (songs), to produce high-quality stereo sound. The success of 

audio CD (or CD-Digital Audio) has been key for the growth and 

success of CD-ROM and other CD formats.

bit: 

The 1 or 0 that represents the smallest piece of data. Bits are used 

mostly when dealing with bandwidth rates (bits/sec), graphics resolutions, and related topics.

byte: 

A string of 8 bits, operated upon as a unit. Bytes are typically used as 

a measure of file size or storage capacity. 

CD (Compact Disc):

An optical disc. CD is a term loosely used when describing a variety 

of compact disc formats, from the production (mass-produced) audio 

and data discs, to the write-once “recordable” versions (CD-R) or 

write-many "rewritable" versions (CD-RW) CDs. The standard CD 

can hold about 650MB of data.
30 Fred R. Byers

CD+G (Compact Disc plus Graphics):

Primarily used for karaoke, this type of CD embeds graphical data 

with the audio data, allowing video pictures to be displayed periodically as music is played. A special player is needed to read and display the information. 

CD-I (Compact Disc-Interactive):

A compact disc format designed to allow interactive multimedia applications (digital audio and video, video games, and software applications) to be run on a player attached to a television. 

CD-R (Compact Disc-Recordable):

A version of CD on which data can be recorded but not erased. An 

organic dye-based material is used to hold data that are written to it 

by a laser.

CD-ROM (Compact Disc-Read Only Memory):

An extension of the compact disc digital audio format that allows 

computer data to be stored. 

CD-ROM drive:

A peripheral device attached to a computer that allows it to read and 

play all CDs.

CD-RW (Compact Disc-ReWritable): 

A version of CD on which data can be recorded and erased and rerecorded in the same physical location of the disc. A phase-changing 

metal alloy film is used to hold the data that are written to it by the 

laser.

content: 

Audio, video, photographic images, graphics, interactive games, 

computer applications, documents, files, databases, etc.; understandable information made up of data stored in a digital format. 

copy: 

(noun) Content that has been read from a source medium and written to another medium or to a separate space on the same medium. 

(verb) To read data from a source, leaving the source data unchanged 

at the source, and to write the same data elsewhere, though the 

new medium may be in a physical form that differs from that of the 

source.

data: 

Pieces of information from which “understandable information” 

is derived. In this guide, data refers to the bits (1, 0) recorded in the 

disc, from which applications or understandable information are 

derived. 
 

 

 

 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 31

data area:

The space on a CD or DVD where the digital content is located. 

data layer: 

The layer on an optical disc that holds data as marks or pits. They

affect the amount of laser light that is reflected back to the laser photosensor.

dielectric layer: 

A layer on both sides of the phase-changing film data layer in rewritable CDs and DVDs (RW and RAM) that rapidly cools the phasechanging film, allowing heated marks to remain crystallized. 

digital: 

The binary coding scheme generally used in computer technology to 

represent data as binary bits (1s and 0s). Digital information is often 

contrasted to analog information. Analog information can be digitized by sampling. 

double-layered DVD: 

A DVD that has two metal data layers, allowing for twice the storage 

capacity over single-layered DVDs.

disc drive: 

A computer peripheral device that reads, or reads and writes, specific discs. 

DVD: 

Once stood for Digital Video Disc or Digital Versatile Disc, now just 

DVD. The next generation of optical disc storage technology after 

the CD. A DVD is the same physical size and shape as a CD, but has 

a higher density and gives the option for data to be double-sided or 

double-layered in the disc.

DVD-Audio: 

An audio-only storage format similar to CD-Audio. DVD-Audio 

differs, however, in offering 16, 20 and 24-bit samples at a variety 

of sampling rates from 44.1 to 192KHz, compared with 16 bits and 

44.1KHz for CDs. The latest audio format more than doubles the 

fidelity of a standard CD. DVD-Audio discs can also contain music 

videos, graphics, and other information.

DVD-R (DVD-Recordable, sometimes referred to as DVD minus R):

A version of DVD on which data can be recorded, but not erased, 

by a disc drive. An organic, dye-based material is used to hold data 

that are written to it by a laser. DVD-R provides secure recording for 

volumes of information that cannot be accidentally or intentionally 

altered. DVD-R has a capacity of 4.7 GB. There are two versions of 

DVD-R:
32 Fred R. Byers

1. DVD-R (A) (DVD-Recordable for Authoring):

A format for professional content developers and software produc-

ers. Primarily used to create master discs that will be mass-produced 

by software houses and multimedia/video postproduction facilities.

2. DVD-R (G) (DVD-Recordable for General use) and DVD+R 

(DVD plus Recordable):

A format for general recording of all types of content: audio, video, 

and data. Compatible with most DVD-Video players and DVD-ROM 

drives.

The differences between DVD-R and DVD+R are as follows:

—DVD+R uses a different technique from DVD-R in how the laser 

follows the disc track while writing data to the disc. A writer discdrive is generally capable of writing to one type of disc but some 

may be capable of writing to both types. All DVD drives should read 

both DVD-R and DVD+R.

—DVD-R uses constant linear velocity (CLV) for the disc rotation; 

DVD+R can use CLV or constant angular velocity (CAV) for the disc 

rotation. CAV allows for easier random access of data on the disc.

—DVD+R can provide lossless linking of new data added from mul-

tiple recording sessions.

DVD-RAM (DVD-Random Access Memory): 

A rewritable DVD. It is a cartridge-based, or, more recently, car-

tridge-less optical disc for data recording and playback. Data can 

be recorded and erased up to 100,000 times, making the DVD-RAM 

a virtual hard disk. DVD RAM uses a phase-change data layer to 

record data written to it by a laser. Current DVD-ROM drives and 

DVD-Video players cannot read DVD-RAM media. 

DVD-ROM (Read Only Memory): 

Typically, an optical disc used for storing data, interactive sequences, 

audio, and video. DVD-ROMs run in DVD-ROM, DVD-R, DVD-RW, 

or DVD-RAM drives, but not in DVD-Video players connected to 

televisions and home theaters. However, most DVD-ROM drives will 

play DVD-Video movies if the associated software is installed in the 

computer.

DVD-RW (sometimes referred to as DVD minus RW, DVDReWritable):

The DVD-RW is similar to DVD-RAM except that its technology fea-

tures a sequential read-write access more like a phonograph than a 

hard disk. Its read-write capacity is 4.7 GB, and it can be re-written 

to about 1,000 times. For general recording of all types of content, 

for audio, for video recording and editing, and for random data re-

cording. Compatible with most DVD-Video players and DVD-ROM 

drives. 

DVD+RW (DVD plus RW), (DVD-ReWritable): 

For general recording of all types of content, for audio, for video recording and editing, and for random data recording. Compatible 

with most DVD-Video players and DVD-ROM drives.
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 33

The differences between DVD-RW and DVD+RW are as 

follows:

—DVD+RW uses a different technique from DVD-RW in how the 

laser follows the disc track while writing data to the disc. A writer 

disc-drive is generally capable of writing to one type of disc but 

some may be capable of writing to both types. Most newer DVD 

drives should read both DVD-RW and DVD+RW.

—DVD-RW uses constant linear velocity (CLV) for the disc rotation; 

DVD+RW can use CLV or constant angular velocity (CAV) for the 

disc rotation. CAV allows for easier random access of data on the 

disc.

—DVD+RW can provide lossless linking of new data inserted or 

added from multiple recording sessions.

DVD Video: 

Used for viewing movies and for other visual entertainment, DVD 

Video is a popular format for high-quality MPEG2 or MPEG4 video 

and digital surround sound. It enables multilanguage, multisubtitling, and other advanced user features. The total capacity is 17 GB if 

two layers are used on both sides of the disk.

emulation technology:

Software or hardware that gives a computer, device, or program 

the ability to mimic the function of another computer, device, or 

program. 

format: 

Pre-established layout for data. 

hub:

The area around the central hole of an optical disc, also called the 

clamping area. The spindle of the drive clamps the disc by this hub, 

which should fit precisely to provide reliable centering and eliminate 

flutter as it transfers the rotational movement imparted by the motor. 

While CD products use this area for serial number and other replication plant production codes, double-sided DVDs will use it for identification information as well. 

information: 

Meaningful expression or interpretation of data. 

jewel case: 

A clear plastic hinged container used to package and store a compact 

disc or DVD. It typically includes a plastic tray to hold the disc, an 

inlay card for labeling, and, often, a booklet in the front of the case.

lacquer layer: 

A very thin layer applied to CDs to protect the metal layer from exposure to the environment. It also provides limited protection from 

writing on or labeling of the disc.
 

 

34 Fred R. Byers

laser photosensor: 

A component of an optical disc drive that senses whether or not it is receiving laser light of a particular frequency with a detectable intensity.

layer:

A single thickness or stratum within a disc. 

life expectancy (LE):

The number of years the disc is expected to be useful. The life of a 

disc is considered at its end when the error rate exceeds a predermined limit, as measured before the error correction process, even if 

the disc is still playable and the errors are not noticeable to the user.

mark: 

A low reflectance feature of a recording layer representing data that 

can be sensed by an optical system. 

media: 

Plural of medium

medium: 

Material on which data are or may be recorded, such as paper, 

punched cards, magnetic tapes, magnetic disks, or optical discs.

metal layer: 

The layer in optical discs that reflects the laser beam back to the laser 

photosensor. Aluminum, gold, silver, or silver alloy are generally 

used depending on the type of disc.

mirror band:

Slender ring of highly reflective silver that extends from the outer 

edge of the clear inner hub at 38 mm to the inner edge of the main 

printable area of the disc at 46 mm.

optical disc: 

A plastic disc that is "written" (encoded) and "read" using a laser optical device. The disc contains a highly reflective metal and uses bits 

to represent data by containing areas that reduce the effect of reflectance when illuminated with a narrow-beam source, such as a laser 

diode. The bits (data) are stored sequentially on a continuous spiral 

track starting from near the center of the disc and going to the outer 

edge.

original: 

The first representation or generation of specific content or an object.

organic dye (dye polymer): 

A photosensitive organic chemical located between the polycarbonate substrate and metal layers and comprising the data layer of a recordable CD or DVD. The dye darkens when exposed to intense light 

(laser) of a particular wavelength.
 

Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 35

oxide-dull: 

The less reflective state of a metal caused by oxidation.

oxidation: 

A chemical reaction between oxygen and another substance, causing 

the original substance to have its properties altered. In the case of 

aluminum, oxidization reduces its reflectivity. 

phase-changing film: 

A metal alloy (silver, indium, antimony, and tellurium), sandwiched 

between two dielectric layers and located between the polycarbonate 

substrate and metal layers. It is the data layer of rewritable (RW and 

RAM) CDs and DVDs. Data is written to this layer after a laser beam 

heats the film, causing crystallization (a phase change) to occur. The 

crystallization remains intact because of rapid cooling caused by the 

dielectric layer on both sides of the film.

photochemical reaction: 

The chemical reaction in CD-R and DVD-R discs resulting from the 

interaction of the organic dye and laser light. The interaction results 

in a change of property of the organic dye in the areas exposed to 

the laser light. These areas are known as bits or data that have been 

“written” into the organic dye.

playback system:

A set of devices that can play or display disc information.

polycarbonate substrate: 

The transparent physical layer that makes up most of an optical disc. 

It also provides mechanical support through which a laser can access 

an information layer. 

pre-recorded disc:

A replicated disc, also called ROM disc. Generally, commercially 

available discs with content recorded on them during manufacturing.

preservation: 

(The definition is slightly adapted from the National Archives and 

Records Administration)

Preservation encompasses the activities that prolong the usable 

life of materials. Preservation activities are designed to minimize 

the physical and chemical deterioration of materials and to prevent 

the loss of informational content. These activities include providing a stable environment for materials of all media types, using safe 

handling and storage methods, duplicating unstable materials (e.g., 

nitrate film, thermofax) to stable media, copying potentially fragile 

materials into a usable format (e.g., microfilming or digitization), 

storing materials in housings made from stable materials (for example, document boxes made from "acid-free" paperboard), repairing 

documents to maintain their original format, establishing a pest con-
36 Fred R. Byers

trol program, and instituting a disaster recovery plan that includes 

plans for emergency preparedness and response.

pressed discs: 

Mass-produced, replicated discs (usually perecorded, commercially 

available discs). The data on these discs are molded as an integral 

part of the polycarbonate substrate during the manufacturing process by applying a metal layer (aluminum) to the side of the polycarbonate substrate containing the “land/bit” form. Also called ROM or 

replicated disc.

read: 

An operation that results in the flow of data from an object (CD, 

DVD) to a subject (CD drive, DVD drive).

record: 

To write data on a medium, such as magnetic tape, magnetic disk, or 

optical disc.

recordable: 

Media that data can be written to. Among optical discs, examples are 

CD-R, DVD-R/+R, CD-RW, DVD-RW/+RW, and DVD-RAM.

Red Book for CD specifications:

Document developed by Sony and Philips in 1980 that provides the 

first specifications for standard compact discs (CD). 

reflectance (reflectivity):

Proportion of incident light that is returned from a reflective surface. 

removable storage: 

Media or hardware used for storing data (content) that is easily removable from, and that can be stored separately from, its associated 

hardware. Examples are CDs and DVDs.

replicated disc:

Generally, a commercially available disc on which content was recorded during the manufacturing process. Also called ROM disc.

rewritable (RW): 

Recordable storage medium that can be overwritten multiple times, 

normally without pre-erasure. Examples are CD-RW, DVD-RW, 

DVD+RW, and DVD-RAM. 

RH: 

Relative humidity 

ROM:

Read only memory. Generally, a commercially available disc on 

which the content was recorded during the manufacturing process. 

Also called replicated disc.
Care and Handling of CDs and DVDs—A Guide for Librarians and Archivists 37

single-sided: 

A disc on which data can be read or written to (recordable discs) 

from one side only.

single-layered DVD: 

A DVD that contains only one metal and data layer, on one or both 

sides. 

slimline case: 

A slimmer version of the jewel case. Unlike the jewel case it does not 

contain the plastic tray, but instead uses an inlay card (J-card). Primarily used for audio discs. 

snapper case:

A plastic DVD case with cardbard cover that is snapped shut and 

held in place by a plastic lip. An alternative to the amaray case for 

storage of pre-recorded DVDs.

storage: 

Retrievable retention of data. Electronic, electrostatic, electrical, hardware or other elements (media) into which data may be entered, and 

from which data may be retrieved, as desired. Also, a facility or place 

that houses hardware or media.

storing: 

The action of holding something (CDs, DVDs) in storage.

UV light: 

Light found between the end of the visible light spectrum (violet, 400 

nm wavelength) and the beginning of the X-ray spectrum (100 nm 

wavelength). Common sources include solar rays and fluorescent 

black lights.

Video CD (V-CD):

A standard for displaying full motion pictures with associated audio on CD. The video and sound are compressed together using the 

MPEG 1 standard and recorded onto a CD Bridge disc.

WORM:

“Write-Once-Read-Many” recording on non-erasable blank media 

that contain pre-stamped grooves to guide a write laser. 

write: 

To record data onto a recordable or rewritable media from a disc 

drive.

write-once:

A recordable storage medium that cannot be erased or re-written. 

Optical disc examples are: CD-R, DVD-R, DVD+R. The R indicates 

recordable disc.
38 Fred R. Byers

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