Source : WordNet®

hard disk
     n : a rigid magnetic disk mounted permanently in a drive unit
         [syn: {hard disc}, {fixed disk}]

Source : Free On-Line Dictionary of Computing

hard disk
     
         (In contrast to {floppy disk}).  One or more rigid
        {magnetic disks} rotating about a central axle with associated
        read/write heads and electronics, used to store data.  Most
        hard disks are permanently connected to the drive (fixed
        disks) though there are also {removable disks}.
     
        High speed disks have an {access time} of 28 milliseconds or
        less, and low-speed disks run 65 milliseconds or more.  The
        higher speed disks also transfer their data faster than the
        slower speed units.
     
        Each surface of each disk is divided into a number of evenly
        spaced concentric circular {tracks}.  The set of all tracks at
        a given radius on all surfaces (the tracks which can be
        accessed without moving the heads) are known as a {cylinder}.
        Each track is divided into {sectors}.
     
        Disk drives are commonly characterised by the kind of
        interface used to connect to the computer, e.g. {ATA}, {IDE},
        {SCSI}.
     
        See also {winchester}.
     
        {Suchanka's PC-DISK library (http://www.pc-disk.de/)}.
     
        (1999-01-07)