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 ?
NASDAQ: MDCD), the leader in CD ROM networking, today announced the move to ultra-performance 12X-speed CD ROM drives for its CD Net CD ROM server and CD NetROM disc array product lines.
With CD IntraNet Software, users for the first time can launch a complete range of CD applications -- without ever exiting their Web browsers -- and access hybrid CD ROMs, in which compact disc files are combined with information retrieved over the Internet, World Wide Web or dial-up services.
CD Net Plus Software is also bundled with Meridian's plug-and-play CD Net integrated network servers, supporting up to 56 high-performance CD ROM drives per server.
1 Software includes Meridian's industry-unique CD Net Tools, an easy-to-use graphical interface that lets NetWare managers quickly evaluate server status conditions, isolate troublesome drives and tune CD ROM throughput for optimal system performance.
Designed for serious system administration, CD Net Tools Pro provides drill-down access to detailed drive-level performance information and usage statistics for each CD ROM drive in every server.
The software toolkit allows an administrator to monitor how the CD server is accessed by users, providing the ability to assess CD ROM usage and system performance and easily troubleshoot problematic drives.
About ten percent of CD ROM titles are published in-house for backup and distribution of proprietary information, such as financial records," said Rattazzi.
Information and reference products will continue to generate most of the CD ROM industry's title revenue.
For those who use CD ROM-based databases or graphics-intensive applications, 20X and 24X CD ROM drives deliver smoother full-motion video and animation than older, slower drives.