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Definition: disk


A storage device that uses rotating platters divided into sectors that hold a fixed amount of data. The sectors are stored in tracks that are recorded in concentric circles on the platter. When a sector is read or written, a mechanical access arm moves to the required track (see access arm).

Invented in the 1950s and the primary storage medium since the 1970s, the disk has slowly but surely given way to solid state drives (SSDs) that have no mechanical parts. See sector, hard disk, magnetic disk, SSD, optical disc, CD-ROM, DVD, floppy disk, RAMAC and DASD.




Disk and Memory Work Together
On the disk, data are stored in sectors, which hold a chunk of data (typically 4,096 bytes) and are the smallest unit that can be read or written. Memory (RAM) is like a checkerboard, each square holding one byte. In RAM, the contents of any single byte or group of bytes can be calculated, compared and copied independently. See storage vs. memory and byte addressable.





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