Standard

There are several formats used for data stored on compact discs, known collectively as theRainbow Books. These include the original Red Book standards for CD audio, White Book andYellow Book CD-ROM. The ECMA-130 standard, which gives a thorough description of the physics and physical layer of the CD-ROM, inclusive of cross-interleaved Reed-Solomon coding(CIRC) and eight-to-fourteen modulation (EFM), can be downloaded from ECMA.^[2]

ISO 9660 defines the standard file system of a CD-ROM, although it is due to be replaced byISO 13490 (which also supports CD-R and multi-session). UDF extends ISO 13346 (which was designed for non-sequential write-once and re-writeable discs such as CD-R and CD-RW) to support read-only and re-writeable media and was first adopted for DVD. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito.

CD-ROM drives are rated with a speed factor relative to music CDs (1× or 1-speed which gives a data transfer rate of 150 KiB/s). 12× drives were common beginning in early 1997. Above 12× speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 30× at the outer edge of the disc with the same rotational speed as a standard constant linear velocity (CLV) 12×, or 32× with a slight increase. However due to the nature of CAV (linear speed at the inner edge is still only 12×, increasing smoothly in-between) the actual throughput increase is less than 30/12 - in fact, roughly 20× average for a completely full disc, and even less for a partially filled one.

Problems with vibration, owing to e.g. limits on achievable symmetry and strength in mass produced media, mean that CDROM drive speeds have not massively increased since the late 90s. Over 10 years later, commonly available drives vary between 24× (slimline and portable units, 10× spin speed) and 52× (typically CD- and read-only units, 21× spin speed), all using CAV to achieve their claimed "max" speeds, with 32× through 48× most common. Even so, these speeds can cause poor reading (drive error correction having become very sophisticated in response) and even shattering of poorly made or physically damaged media, with small cracks rapidly growing into catastrophic breakages when centripetally stressed at 10,000 - 13,000rpm (i.e. 40-52× CAV). High rotational speeds also produce undesirable noise from disc vibration, rushing air and the spindle motor itself. Thankfully, most 21st century drives allow forced low speed modes (by use of small utility programs) for the sake of safety, accurate reading or silence, and will automatically fall back if a large number of sequential read errors and retries are encountered.

Other methods of improving read speed were trialled such as using multiple pickup heads, increasing throughput up to 72× with a 10× spin speed, but along with other technologies like 90~99 minute recordable media and "double density" recorders, their utility was nullified by the introduction of consumer DVDROM drives capable of consistent 36× CDROM speeds (4× DVD) or higher. Additionally, with a 700mb CDROM fully readable in under 2½ minutes at 52× CAV, increases in actual data transfer rate are decreasingly influential on overall effective drive speed when taken into consideration with other factors such as loading/unloading, media recognition, spin up/down and random seek times, making for much decreased returns on development investment. A similar stratification effect has since been seen in DVD development where maximum speed has stabilised at 16× CAV (with exceptional cases between 18× and 22×) and capacity at 4.3 and 8.5GiB (single and dual layer), with higher speed and capacity needs instead being catered to by Blu-Ray drives.