CD-ROM
(Compact Disc Read
Only Memory) A compact disc format used to hold text, graphics and hi-fi stereo
sound. It's like an audio CD, but uses a different track format for data. The audio CD player cannot
play CD-ROMs, but CD-ROM players usually play audio CDs and have output jacks for a headphone or
amplified speakers.
CD-ROMs hold in excess of 650MB of data, which
is equivalent to about 250,000 pages of text or 20,000 medium-resolution images.
A CD-ROM drive (player, reader) connects to a controller card, which is plugged into one of the
computer's expansion slots. Earlier drives used a proprietary interface and came with their own card,
requiring a free expansion slot in the computer. Today, most CD-ROMs use the SCSI interface and can
be daisy chained to an existing SCSI controller. Increasingly, CD-ROM drives are built with the IDE
interface, which allows them to connect to the same Enhanced IDE controller that the hard and floppy
disks are attached to.
Earlier CD-ROM drives transferred data at 150KB per second. Double, triple and quad-speed drives
provide 2x, 3x and 4x the 150KB transfer rate. 40x speed drives increase transfer to
6MB/second. For
full-motion video, at least 8x speed is required. Access times run from a slow half second
to under 200 milliseconds.
Audio and data reside on separate tracks and cannot be heard and viewed together on earlier
drives that are not CD-ROM XA compliant. Unlike other optical disks, CD-ROMs, as well as audio CDs,
use a spiral recording track just like the "ancient" phonograph record. See CD-ROM XA, CD-I
and DVI.
CMOS (Complimentary Metal Oxide Semiconductor)
A battery-powered chip in 80286 (and more advanced) computers that preserves basic data about the system's hardware. Information such as the number and types of disks, amount of RAM, and keyboard type is stored in a CMOS chip. This information appears on your computer's "setup screen" which can be displayed during startup.
CPU (central processing unit)
The portion of a computer that performs computations, executes instructions and transfers information between all parts of the computer. Microcomputers contain single-chip central processing units, or microprocessors.
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