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 SCSI Express 16X CD-ROM line is scheduled to begin shipping in July, 1997.
1" SVGA TFT CD-ROM 24X with AutoPlay(tm) 16X CD-ROM OS Microsoft Windows(R)95 Microsoft Windows 95 Software Microsoft Office SBE Microsoft Office SBE Modem 56kbs fax/modem(b) 56kbs fax/modem(b) Old Price $4599 $2399 New Price $3987 $1999
Based on the initial success of the first two products, Fry's agreed to add a third product, the MagicSpin 16X CD-ROM shortly thereafter.
44GB hard drive, 16X CD-ROM, one "swappable" bay for either a floppy drive or a CD-ROM, Microsoft(R) Windows(R) 95 operating system (upgradable to Microsoft's Windows NT(R)) and a 12.
00 210 Mhz PowerPC 604e; 64 MB RAM; 2 GB AV UltraSCSI 5400 RPM Hard Drive; 16X CD-ROM Drive; 1 MB Level 2 Cache; Ultra SCSI up to 20MB/sec; 3D Graphics acceleration with 2MB Video DRAM based graphics; Mac 15-pin & SVGA Connectors; 3 PCI expansion slots; built-in Ethernet (AAUI & 10BaseT); extended keyboard; mouse; $1,000 software bundle; low profile enclosure (add $100.
The PowerCenter Pro 240, which comes with a PowerPC 604e running at 240 MHz with a 60 MHz bus; 32 MB RAM; 2 GB 5400 RPM Ultra SCSI Hard Drive; 16X CD-ROM drive; 2 MB of video DRAM; built-in 3D hardware graphics acceleration; 1 MB Level 2 upgradeable cache; Ultra SCSI up to 20 MB/sec; extended keyboard and mouse; and more than $1,000 in bundled software, drops in price from $2,595 to $2,495 for the low profile enclosure and from $2,695 to $2,595 for the mini tower enclosure.
8-inch viewable), a 16X CD-ROM drive, an Ethernet 10/100 card, Windows95 and a choice of software suites.