CD-ROM

The CD-ROM (an abbreviation for "Compact Disc Read-Only Memory") is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. A CD-ROM is a flat, metallized plastic disc with digital information encoded on it in a spiral from the center to the outside edge. The CD-ROM Yellow Book standard was established in 1985 by Sony and Philips. Microsoft and Apple Computer were early enthusiasts and promoters of CD-ROMs. John Sculley, CEO of Apple at the time, said as early as 1987 that the CD-ROM would revolutionize the use of personal computers.

CD-ROM drives

CD-ROMs are read using CD-ROM drives and written with CD recorders (often referred to as "burners"). CD-ROM drives—now almost-universal on personal computers—may be connected to the computer via an IDE (ATA) interface, a SCSI interface or a proprietary interface, such as the Panasonic CD interface. Most CD-ROM drives can also play audio CDs and Video CDs with the right software.

Related Topics:
CD recorder - IDE - ATA - SCSI - Panasonic CD interface - Audio CDs - Video CD

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CD-ROM drives are rated with a speed factor relative to music CDs: 1x or 1-speed which gives a data transfer rate of 150 kilobytes per second in the most common data format. For example, an 8x CD-ROM data transfer rate would be 1.2 megabytes per second. Above 12x speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 20x but due to the nature of CAV the actual throughput increase over 12x is less than 20/12. 20x was thought to be the maximum speed due to mechanical constraints until February 1998, when Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing system to balance the spinning disc in the drive to reduce vibration and noise. As of 2004, the fastest transfer rate commonly available is about 52x or 7.62 megabytes per second, though this is only when reading information from the outer parts of a disc. Future speed increases based simply upon spinning the disc faster are particularly limited by the strength of polycarbonate plastic used in CD manufacturing. Speed improvements can however still be obtained by the use of multiple laser pickups as demonstrated by the Kenwood TrueX 72x which uses seven laser beams and a rotation speed of approximately 10x.

Related Topics:
Constant angular velocity - 1998 - Samsung - Bearing - As of 2004 - Kenwood - TrueX

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CD-Recordable drives are often sold with three different speed ratings, one speed for write-once operations, one for re-write operations, and one for read-only operations. The speeds are typically listed in that order; ie a 12x/10x/32x CD drive can, CPU and media-permitting, write to CD-R disks at 12x speed (1.76 megabytes/s), write to CD-RW discs at 10x speed (1.46 megabytes/s), and read from CD discs at 32x speed (4.69 megabytes/s).

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The 1x speed rating for CDs (150 kilobytes/s) is not to be confused with the 1x speed rating for DVDs (1.32 megabytes/s).

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Some of the initial versions of CD Drives had a mechanism different from the tray or slot loaders of modern day drives. They could read CDs only when they were inserted in special cartridges. The "CD Caddy" resembled the floppy disk because of its protective casing. It, however, never caught on.

Related Topics:
Cartridge - Floppy disk

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