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 ?
Another penalty allowed Deakin to double the lead on 74 minutes, with the midfielder slotting home after Sam Smith brought down Town striker Justin Rowe.
Still Southampton refused to lie down and Hughes smashed a trademark volley against the crossbar, but United did not heed that warning and on 74 minutes the visitors pegged them back again.
The FZ-FV1 Video CD Adaptor, available this spring, uses the MPEG-1 Video CD standard to allow up to 74 minutes of VHS-quality video along with 74 minutes of digital quality audio on a compact disc.
PST (10:04 GMT) from this West Coast launch site, releasing a national security payload into transfer orbit 74 minutes later.
When Maguire, the new tournament favourite after Ronnie O'Sullivan's defeat by Mark Allen, potted the black to win it 70-56, they had taken 74 minutes 58 seconds.
Jay Bothroyd blasted the Welsh side ahead after 74 minutes.
Anderson slotted his second after 74 minutes but Craig Feroz rolled the ball home late on to set up a tense finish.
After the break the Daggers responded and the equaliser came after 74 minutes when Matt Ritchie smashed home a brilliant left-footed volley.
Gregg Cooper was on the scoresheet on 74 minutes and Matthew Cowling then completed the scoring.
Accies dominated after the break but it was 74 minutes before James McCarthy put them back in front with a 12-yard shot.
That didn't stop Coseley from creating the better chances before they drew level on 74 minutes when Antonio Gamborne stole in unmarked to fire home.
But it was the visitors who took the lead after 74 minutes when Antony Kay fired home, only for the home side to level matters through Craig Disley seven minutes later.