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Desktop Video AGOCG Report


CD-ROM is an important enabling technology for DTV. New PCs are increasingly being sold with their system software and documentation on CD-ROM and it is becoming the norm to sell PCs with a CD-ROM drive as part of the package.

A CD-ROM can hold about 650 megabytes of data, the equivalent to hundreds of floppy disks. The data on a CD-ROM is accessed much faster than a tape, but they are 10 to 20 times slower than hard disks. However, the use of software cache techniques can improve apparent access rates. Most CD-ROM drives have internal RAM caches which buffer data to boost the throughput, but they also benefit from system level caches (e.g., on a Macintosh there is a system RAM cache controlled by the Memory Control Panel).

For some years CD-ROM has been reasonably stable. Recently, however, there has been a spate of developments, spawning terms like CD-ROM XA2, Mode 1, Mode 23, dual speed, MultiSpin4, and multi-sessional capability. There has been a consequent explosion of titles, further encouraged by the fact that Apple has launched the AppleCD 300, which it is selling at cost price in order to seed the CD-ROM drive market.

Now that much CD-ROM based software contains a lot of sound, graphics and animations, the CD-ROM drive hardware has had to catch up. One of the ways this has been done is by introducing dual speed technology, which spins the CD at twice the normal speed to boost how fast some data can be read, while retaining a slower speed to play audio.5

While it might be thought that higher speed was advantageous, this is not necessarily the case. Certainly, dual speed capability helps with operations such as copying and opening files, but access time (such as that taken searching for files) is not significantly decreased. Also, some QuickTime movies do not benefit much from the doubling of data transfer rates because they have been optimised for the standard single-speed 150 K/sec CD-ROM drives. However, as movies begin to be developed for the faster drives, greater frame rates will mean better video motion.

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