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.

A person in charge of archives administration, including preservation.

(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.

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.

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.

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 re-recorded 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.

Audio, video, photographic images, graphics, interactive games, computer applications, documents, files, databases, etc.; understandable information made up of data stored in a digital format.

(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.

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.

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 phase-changing film, allowing heated marks to remain crystallized.

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.

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.

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:

  1. DVD-R (A) (DVD-Recordable for Authoring):
    A format for professional content developers and software producers. 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 disc-drive 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 multiple recording sessions.

DVD-RAM (DVD-Random Access Memory):
A rewritable DVD. It is a cartridge-based, or, more recently, cartridge-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, DVD-ReWritable):
The DVD-RW is similar to DVD-RAM except that its technology features 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 recording. 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.
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.

Pre-established layout for data.

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.

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.

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.

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.

A low reflectance feature of a recording layer representing data that can be sensed by an optical system.

Plural of 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.

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.

The less reflective state of a metal caused by 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.

(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 control 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.

An operation that results in the flow of data from an object (CD, DVD) to a subject (CD drive, DVD drive).

To write data on a medium, such as magnetic tape, magnetic disk, or optical disc.

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.

Relative humidity

Read only memory. Generally, a commercially available disc on which the content was recorded during the manufacturing process. Also called replicated disc.

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.

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.

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.

“Write-Once-Read-Many” recording on non-erasable blank media that contain pre-stamped grooves to guide a write laser.

To record data onto a recordable or rewritable media from a disc drive.

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.