Source : Free On-Line Dictionary of Computing

DOS/360
     
         The {operating system} announced by {IBM}
        at the low end for the {System/360} in 1964 and delivered in
        1965 or 1966.
     
        Following the failure of {OS}, IBM designed DOS for the low
        end machines, able to run in 16KB(?) and 64KB memory.
     
        DOS/360 used three {memory partitions}, but it had no serious
        {memory protection}.  The three partitions were not
        specialised, but frequently one was used for {spooling}
        {punched cards} to {disk}, another one for {batch job}
        execution and another for spooling disk to printers.
     
        With DOS/VS, introduced in 1970, the number of partitions was
        increased, {virtual memory} was introduced and the minimum
        memory requirements increased.
     
        Later they released DOS/VSE and ESA/VSE.  DOS/360 successors
        are still alive today (1997) though not as popular as in the
        late 1960s.
     
        Contrary to the Hacker's {Jargon File}, {GECOS} was not copied
        from DOS/360.
     
        (1997-09-22)