Source : Free On-Line Dictionary of Computing

MS-DOS
     
         /M S doss/ Microsoft Disk Operating System
        (Or "{DOS}", "{MS-DOG}", "{mess-dos}") {Microsoft
        Corporation}'s {clone} of {CP/M} for the {8088} crufted
        together in 6 weeks by hacker Tim Paterson, who is said to
        have regretted it ever since.
     
        MS-DOS is a single user {operating system} that runs one
        program at a time and is limited to working with one megabyte
        of memory, 640 kilobytes of which is usable for the
        {application program}.  Special add-on {EMS} memory boards
        allow EMS-compliant software to exceed the 1 MB limit.
        Add-ons to DOS, such as {Microsoft Windows} and {DESQview},
        take advantage of EMS and allow the user to have multiple
        applications loaded at once and switch between them.
     
        Numerous features, including vaguely {Unix}-like but rather
        broken support for subdirectories, {I/O redirection}, and
        {pipelines}, were hacked into MS-DOS 2.0 and subsequent
        versions; as a result, there are two or more incompatible
        versions of many system calls, and MS-DOS programmers can
        never agree on basic things like what character to use as an
        option switch or whether to be case-sensitive.  The resulting
        mess is now the highest-unit-volume {operating system} in
        history.  It is used on many {Intel} 16 and 32 bit
        {microprocessors} and {IBM PC} compatibles.
     
        Many of the original DOS functions were calls to {BASIC} (in
        {ROM} on the original {IBM PC}), e.g. Format and Mode.  People
        with non-IBM PCs had to buy {MS-Basic} (later called
        {GWBasic}).  Most version of DOS came with some version of
        BASIC.
     
        Also know as PC-DOS or simply as DOS, which annoys people
        familiar with other similarly abbreviated operating systems
        (the name goes back to the mid-1960s, when it was attached to
        {IBM}'s first disk operating system for the {IBM 360}).  Some
        people like to pronounce DOS like "dose" or to compare it to a
        dose of brain-damaging drugs (a slogan button in wide
        circulation among hackers exhorts: "MS-DOS: Just say No!").
     
        [{Jargon File}]
     
        (1998-07-19)