Technology: A Glossary of CD Terms

A-Time: (or absolute time) In an audio CD, the time elapsed since the beginning of the disc.

BLER: Block Error Rate. Measures how many errors occur in a given time period while a disc is playing, usually an average over a ten-second time span.

Blue Book: The official standard which dictates the format of CD Extra discs.

Buffer Underrun: A buffer underrun occurs when your computer system cannot keep up the steady stream of data required for CD recording. The CD recorder has an internal memory buffer to protect against interruptions and slowdowns, but if the interruption is so long that the recorder’s buffer is completely emptied, a buffer underrun occurs, writing stops, and most often the recordable CD is ruined.

CD Extra or CD Plus: A multisession disc containing a number of audio tracks in the first session, and one CD-ROM XA data track in the second session.

CD+G: (aka karaoke) A special disc format in which simple graphics and text are stored in the subchannels of an audio disc.

CD-DA: Compact Disc-Digital Audio. The CD-DA standard is known as the Red Book. Audio tracks on CD-DA discs are stored at 44.1 kHz, 16 bits, stereo.

CD-I: A compact disc format (no longer used) developed by Philips, designed to allow interactive multimedia applications to be run on a player attached to a television. The standard defining CD-I is called the Green Book.

CD-R: Compact disc-recordable. When referring to recordable discs (media), “CD-R” is often used to refer to write-once discs, in contrast to CD-RW.

CD-ROM: Compact Disc-Read Only Memory. A standard for compact disc to be used as digital memory media for personal computers. First defined in the Yellow Book.

CD-ROM XA: “XA” stands for Extended Architecture. CD-ROM XA is an extension of the Yellow Book standard, generally consistent with the ISO 9660 logical format.

CD-RW: CD-ReWritable. CD recordable media which can be erased and re-recorded. CD-RW media can only be written in a CD-RW recorder, not in a normal CD recorder, though a CD-RW recorder can also record standard CD-R discs.

CD Text: An audio CD format in which up to 5000 characters of disc information (title, artist, song titles, etc.) is written into the disc Table of Contents. This information is displayed when the disc is played back on CD Text-enabled players.

CD-WO: Compact Disc-Write Once. A rarely-used term for recordable compact disc.

Close Disc: To “close” a recordable disc so that no further data can be written to it. This is done when the last session’s lead-in is written. The next writeable address on the disc is not recorded in that lead-in, so the CD recorder in subsequent attempts to write has no way of knowing where to begin writing. Note: It is NOT necessary to close a disc in order to read it in a normal CD-ROM drive.

Close Session: When a session is closed, information about its contents is written into the disc’s Table of Contents, and a lead-in and lead-out are written to prepare the disc for a subsequent session.

Disc-at-Once: A method of writing CDs in which one or more tracks are written in a single operation, and the disc is closed, without ever turning off the writing laser. Contrast with Track-at-Once. Not all CDrecorders support Disc-at-Once.

Disc Image: A single large file which is an exact representation of the whole set of data and programs as it will appear on a CD, in terms of both content and logical format.

High Sierra Format: The standard logical format for CD-ROM on which the ISO 9660 standard is based; essentially identical to ISO 9660. No longer used.

Hybrid: Under the Orange Book standard for recordable CD, hybrid means a recordable disc on which one or more sessions are already recorded, but the disc is not closed. However, in popular use the term “hybrid” often refers to a disc containing both DOS/Windows and Macintosh software.

Indexes: Indexes provide additional starting points within a single audio track. Not all audio CD players support indexes. Index markers are written into the Q subchannel and are incremented by 1 sequentially during the track.

ISO 9660 Format: The most common international standard for the logical format for files and directories on a CD-ROM. Some other common logical formats such as Joliet and Rock Ridge are extensions of ISO 9660.

ISRC: International Standard Recording Code. Some recorders allow the ISRC to be recorded for each audio track on a disc. The code is made up of: Country Code (2 ASCII characters), Owner Code (3 ASCII characters), Year of Recording (2 digits), Serial Number (5 digits).

Joliet: Joliet is an extension of the ISO 9660 standard, developed by Microsoft to allow CDs to be recorded using long filenames, and using the Unicode international character set. Joliet allows you to use filenames up to 64 characters in length, including spaces.

Lead-In: An area at the beginning of each session on a recordable compact disc which is left blank for the session’s Table of Contents. The lead-in is written when a session is closed, and takes up 4500 sectors on disc (1 minute, or roughly 9 megabytes). The lead-in also contains next writeable address on the disc, so that future sessions can be added (unless the disc is closed).

Lead-Out: An area at the end of a session which indicates that the end of the data has been reached. Writing the lead-out closes the session. CD-ROM drives and CD audio players cannot see the data/audio in a session until the session is closed.

Mixed-Mode Disc: A compact disc including both computer data and CD-DA tracks. The data is all contained in Track 1, and the audio in one or more following tracks. Contrast with CD Extra.

Mount: To install a compact disc so that the computer recognizes its presence and can read data from it.

Multisession: A method of adding data incrementally to a CD in more than one recording session.

On the Fly: To write on the fly means to write directly from source data to CD data without first writing a disc image.

Optimum Power Calibration Area: (OPC Area) A special area near the center of the recordable disc. Before writing a track on a disc, the CD recorder must adjust the amount of power applied to the writing laser to an optimum level for each individual disc. The optimum calibration area is reserved for this purpose.

Orange Book: The Philips/Sony specification for Compact Disc Magneto-Optical (CD-MO) and Write-Once (CD-WO) systems - in other words, the standard by which recordable CDs are recorded.

Packet Writing: A method of writing data on a CD in small increments (contrast with Track-at-Once and Disc-at-Once). Packets can be of fixed or variable length.

PMA: (Program Memory Area) On a recordable disc, an area which “temporarily” contains the Table of Contents information when tracks are written in a session which is not yet closed. When the session is closed, this same data is written in the session lead-in.

Red Book: The Philips/Sony specification for audio (CD-DA) compact discs.

Rock Ridge: An extension of the ISO 9660 file system designed to support UNIX file system information (such as longer filenames and deeper directory structures).

Run-In/Run-Out Blocks: Blocks of data written before and after a packet or a track, to allow the recorder to synchronize with the data on disc, and to finish up interleaved data. Four run-in blocks and two run-out blocks are written for each packet.

Session:As defined in the Orange Book, a recorded segment of a compact disc which may contain one or more tracks of any type (data or audio). In data recording, there is usually only one track per session, but there may be multiple sessions on a disc. In audio recording, all audio tracks should be in a single session. A lead-in and lead-out are recorded for every session on a disc.

Subchannels (or subcodes): Audio CDs have 8 subchannels of non-audio data interleaved with the audio

data, called the P, Q, R, S, T, U, V, and W channels. The P and Q channels are used to tell an audio player how to play back an audio disc. The Q channel contains the index markers.

Table of Contents: For a whole disc or any session within a disc, shows the number of tracks, their starting locations, and the total length of the data area. The TOC does NOT show the length of each track, only its starting point.

Track-at-Once: A method of writing data to disc. Each time a track (data or audio) is completed, the recording laser is stopped, even if another track will be written immediately afterwards.

UDF: Universal Disc Format. A file system for use with packet writing and other recordable optical disc technologies, such as DVD.

UPC: Universal Product Code. With some CD recorders, you may define a thirteen-digit UPC catalog number for the entire disc, which will be written in the disc’s Table of Contents. Also known as EAN.

Volume: Under the ISO 9660 standard, “volume” refers to a single CD-ROM disc. However, “volume” is often used to mean a session on a multisession disc, which is not linked to other sessions.

Yellow Book: The book which sets out the standard developed by Philips and Sony for the physical format of compact discs to be used for information storage (CD-ROM).

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