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.

Capacity

The standard CD-ROM can hold 650-700 megabytes of data. The CD-ROM is popular for distribution of software, especially multimedia applications, and large databases. A CD weighs under an ounce. To put the CD-ROM's storage capacity into context, the average novel contains 60,000 words. Assume that average word length is 10 letters - in fact it is less than 10 - and that each letter occupies one byte. A novel therefore might occupy 600,000 bytes. One CD can therefore contain over 1,000 novels. If each novel occupies half an inch of bookshelf space, then one CD can contain the equivalent of about 15 yards (~16.5 metre) of bookshelf. However textual data can be compressed by more than a factor of ten, using computer compression algorithms (often known as 'zipping'), so a CD-ROM can accommodate at least 100 yards of bookshelf space. In comparison a DVD typically contains 4.7 GB of data or more, depending upon its type. Dual layer DVD+R discs, for example, contain 8.5GB of data for a normal sized (12 cm) disc.

Related Topics:
Megabyte - Software - Multimedia - Database - Novel - Byte - Yard - Metre - Compression algorithms - DVD

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