CD-ROM

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CD-ROM:

see compact disccompact disc
(CD), a small plastic disc used for the storage of digital data. As originally developed for audio systems, the sound signal is sampled at a rate of 44,100 times a second, then each sample is measured and digitally encoded on the 4 3-4 in (12 cm) disc as a series of
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.

CD-ROM

[¦sē¦dē ′räm]
(computer science)

CD-ROM

compact disc read-only memory; a compact disc used with a computer system as a read-only optical disk

CD-ROM

CD-ROM

(Compact Disc-Read Only Memory) A type of CD disc that can only be read, but not recorded. Used to store programs and data files, a CD-ROM holds 650MB or 700MB of data and employs a different recording format than the audio CD (CD-DA), from which it evolved. In the 1990s, the CD-ROM rapidly replaced the floppy disk for software distribution.

An audio CD player cannot read CD-ROMs, but CD-ROM drives can play audio discs. In practice, the term "CD" refers to all CD formats. The phrase "insert the installation CD" really means "insert the installation CD-ROM."

How CD-ROMs Are Made
CD-ROMs are made by "burning" a blank CD-R disc and sending it to a media manufacturer, which creates a master disc that is used to stamp out the required quantity. See CD-R and mini CD.

Pretty Slow in the Beginning
Back in the late 1980s, the first CD-ROM drives transferred data at 150KB per second. By doubling the spindle speed from 530 to 1,060 RPM, the transfer rate doubled to 300KB (2x). For several years thereafter, speeds increased until reaching 48x and higher, making the "1x" drive painfully slow by comparison. For details about speeds, see CD-ROM drives. Access times range from 80 to 150ms. See CD-R, CD-RW, DVD and optical disc.


Caddy Load and Tray Load
Earlier drives used a caddy. The disc must be inserted into the caddy, and the caddy inserted into the drive. Today, drives are caddyless. The disc is placed into a tray.




Caddy Load and Tray Load
Earlier drives used a caddy. The disc must be inserted into the caddy, and the caddy inserted into the drive. Today, drives are caddyless. The disc is placed into a tray.







Reading CDs and CD-ROMs
Digital data are carved into the disc as pits (low spots) and lands (high spots). As the laser shines into the moving pits and lands, a sensor detects a change in reflection when it encounters a transition from pit to land or land to pit. Each transition is a 1. The lack of transitions are 0s. There is only one laser in a drive. Two are used here to illustrate the difference in reflection.







References in periodicals archive ?
The minimum hardware and software requirements for the CD are as follows: a Pentium machine, 16 megabytes of memory, external speakers, a display-size setting of 800 x 600, 16-bit color, 2X CD-ROM drive, Windows 95 with the MM player installed, and a 14-inch monitor.
8.1 min., 8MB (5MB dedicated to mPower); Windows 95/98/ 2000/NT 4.0 min., 486/66 min., Pentium rec., 24MB, SVGA; for both: 175MB hard drive space, 256 colors, 2x CD-ROM drive.
Multimedia PC, 486/33 processor or faster, 8MB RAM, SVGA 640 x 480 video, 2x CD-ROM drive, sound card, Windows 95 or higher.
Requirements: Windows 95/98, 486 Pentium, Windows-compatible sound card; Macintosh System 7.01, 68040 or Power PC; 8 MB of RAM (16 MB for Power PC), color monitor, 2x CD-ROM drive.
HARDWARE & SOFTWARE REQUIREMENTS: IBM-compatible 486, Windows 3.1 or 95, 4 MB RAM, 4 MB hard disk space, 13" VGA monitor, and 2X CD-ROM drive; or Macintosh 68020 processor, System 6.0.8, 4 MB RAM, 13" color monitor, and 2X CD-ROM drive
7.5 min.; Windows 95 min.; for both: 32MB, 256 colors, 60MB hard drive space, 2x CD-ROM drive min.
Requirements: 8 MB of RAM, 2x CD-ROM or faster; Macintosh System 7.0 or higher; Windows 3.1 or higher, sound card.
HARDWARE & SOFTWARE REQUIREMENTS: PC with 486SX processor, 8MB RAM, 2X CD-ROM drive, 256-color SVGA monitor at 640 x 480 pixels, Windows 3.1 or later, Windows-compatible sound card (16-bit recommended), mouse, keyboard, and external speakers, headphones, or stethoscope.