Since its introduction by Sony and Philips in 1983, the compact disc has had a dramatic impact on how people listen to music. With the proliferation of CD-ROMs, the same delivery medium is beginning to affect how we watch movies, swap photographs, and read books. The advantages of CDs include their small size, large data capacity, low manufacturing cost, and physical robustness. The adherence to one hardware standard (the Red Book) has ensured the acceptance of CDs in many fields. However, the number of enhanced standards is ever increasing.
Music CDs allow the storage of up to 74 minutes (though it seems this limit is always tested) of 16-bit stereo sound at a 44.1 KHz sampling rate. CD singles, or CD-3, are smaller (8 cm) and allow for about 22 minutes of music. CD-ROM (Read Only Memory) is an alternate encoding format defined by the Yellow Book. This allows for either 650 MB (12 cm) or 200 MB (8 cm) of storage.
CD-ROM drives are generally capable of reading both music and ROM discs. Most transmit information at 150 K/s. This is a severe bottleneck for video and other high-volume data, so manufacturers (NEC leading the way) have introduced double-speed (300 K/s) drives. In the near future, this rate will likely be doubled again.
Photo-CDs are a Kodak invention which allow the storage of 100 images (each at five resolutions) on one disc. Special players, designed for the home market, plug straight into a TV for viewing. According to Matazzoni, Kodak will soon "provide the ability to put sound, text, graphics, and scripts onto Photo-CD discs" ("CD-ROM Types" 97). With the proper software, this could turn the format into a complete, low-cost, multimedia delivery system. For an introduction to this technology, see McCabe.
Photo-CDs require two further enhancements to drive technology. The first is the ability to read multi-session discs--those which were written to on more than one occasion. The second is XA-compatibility. The XA format compresses audio data and allows faster transfer rates through special storage algorithms. This standard is especially important for multimedia work.
Further standards have proliferated. CD-I (Interactive) allows either 7800 still images, 1.2 hours of hi-fi audio, 19 hours of low-fi audio, or several minutes of partial-screen video (Jonassen 86). CD-R refers to the recordable disc format defined in 1990 by the Orange Book. CD-WO are write-once discs which allow for mastering using relatively inexpensive equipment.
Not all companies have followed the standards proposed by Sony and Philips. Intel and IBM have proposed Digital Video Interactive (DVI) as an alternative to CD-I.
For a further discussion of CD standards, see Meyer.
[1995 update: Quad-speed and faster CD-ROM drives are now common. More interesting, drives for writing CDs may readily be purchased for under $2,000. The hypertext author can now write and publish their own electronic works without the overhead of securing a publishing contract.]