(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 (ORrecORd). (1998-07-08)