Source : WordNet®

disk operating system
     n : an operating system that is on a disk [syn: {DOS}]

Source : Free On-Line Dictionary of Computing

disk operating system
     
         (DOS) The name of a number of {operating
        systems} which include facilities for storing files on disk.
        Such a system must handle physical disk I/O, the mapping of
        file names to disk addresses and protection of files from
        unauthorised access (in a {multi-user} system).
     
        A DOS should present a uniform interface to different storage
        device such as {floppy disks}, {hard disks} and {magnetic
        tape} drives.  It may also provide some kind of locking to
        prevent unintentional simultaneous access by two processes to
        the same file (or {record}).
     
        (1998-07-08)

Disk Operating System
     
         (DOS) The original {disk operating system}
        from {IBM}.
     
        DOS was the low-end OS of choice on the {IBM 360}, the
        high-end system was called just "{OS}".  DOS had a smaller
        {kernel} and less functionality than OS and could run on the
        typical 32K 360/30 and 64K 360/40 class machines.
     
        DOS was a successor to {TOS}.
     
        (1999-01-20)