CDROM FORMATS

8/2/97

CDROM Formats: CDROMs are a rotating storage device that stores data in tiny pits burned into a plastic disk. CDROMs are either read only or write once devices. Different formats are used for audio and digital data. Both use an 8 to 14 modulation RLL-like scheme that is suited to the media characteristics and both use lots of error correction bits. CDROM sectors are 2352 bytes, with 304 audio data bytes per sector on data CDROMs dedicated to additional error detection/correction leaving 2048 data bytes per sector on data CDROMs.

CDROMs come in a number of formats. Many CDROM drives can read a number of different formats. There are two disk sizes used -- an older 580mb disk and a newer 660mb disk. Data itself may be stored in audio format (Compact Disk Digital Audio Standard -- "Red Book") or any of several digital formats ("Yellow book"). Despite the peculiar terminology, Red and Yellow book formats are known to, and available from ANSI. Other formats include "Green book" (CDROM-Interactive); "Orange Book" (Write-Once CDs proprietary to Sony/Phillips); and "Blue Book" for Laser Disk. Various formats exist for intermixing data, audio and video -- CD-I, CDROM/XA. Many CDROM units won't support these.

The most common PC digital formats are High Sierra and ISO-9660 which are very similar. ISO-9660 is essentially a an MSDOS compatible file system format. For example, file names are 8 upper case characters with a 3 character extension. There is a level 2 ISO-9660 format which allows 32 character file names. It is not compatible with MSDOS. There is also a set of "Rock Ridge" extensions to ISO-9660 that support unix file systems on CDROM. Netware 3.11 and above will support these as will many Unix systems. ECMA-167 is an Orange Book compatible Write Once CDROM format that supports Unix file systems, but is not ISO-9660 compatible, Mackintosh CDs are generally recorded using the Mac HFS format which is not compatible with PCs.

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