Compact Disc Read-Only Memory
CD-ROM
CD-ROM drive
(CD-ROM) 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.
CD-ROM is popular for distribution of large databases, software and especially multimedia applications. The maximum capacity is about 600 megabytes. A CD can store around 640 megabytes of data - about 12 billion bytes per pound weight.
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). 12x drives were common in April 1997. 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 but on 1998-02-24, Samsung Electronics introduced the SCR-3230, a 32x CD-ROM drive which uses a ball bearing system to balance the spinning CD-ROM in the drive to reduce noise.
CD-ROM drives may connect to an IDE interface, a SCSI interface or a propritary interface, of which there are three - Sony, Panasonic, and Mitsumi. Most CD-ROM drives can also play audio CDs.
There are several formats used for CD-ROM data, including Green Book CD-ROM, White Book CD-ROM and Yellow Book CD-ROM. ISO 9660 defines a standard file system, later extended by Joliet.