Definition: Hard disk (HD)

Medium for permanent storage of data. Magnetic platters, electronics, and mechanics make up a hard disk. The platters are fixed to a spindle. On each side of a platter there is a read/write head. Each platter is divided into tracks, which is also divided into sectors. A characteristic of hard disks is that the platters and the mechanics are in an airtight enclosure, and the read/write heads do not touch the platters as long as the platters are rotating. See fly height.