hard disk drive

   A storage device that uses a set of rotating, magnetically coated disks called platters to store data or programs. In everyday use, the terms hard disk, hard disk drive, and hard drive are used interchangeably, because the disk and the drive mechanism are a single unit. A typical hard-disk platter rotates at several thousand revolutions per minute, and the read/write heads float on a cushion of air from 10 to 25 millionths of an inch thick so that the heads never come into contact with the recording surface. The whole unit is hermetically sealed to prevent airborne contaminants from entering and interfering with these close tolerances.

   Hard disks range in storage capacity from a few tens of megabytes to several terabytes. The more storage space on the disk, the more important your backup strategy becomes. Hard disks are reliable, but they do fail, and usually at the most inconvenient moment.

   See also high-capacity storage system; mini-hard disk; redundant array of inexpensive disks; single large expensive disk.