Source : WordNet®

mainframe
     n 1: a large digital computer serving 100-400 users and occupying
          a special air-conditioned room [syn: {mainframe computer}]
     2: (computer science) the part of a computer (a microprocessor
        chip) that does most of the data processing; the CPU and
        the memory form the central part of a computer to which
        the peripherals are attached [syn: {central processing
        unit}, {CPU}, {C.P.U.}, {central processor}, {processor}]

Source : Free On-Line Dictionary of Computing

mainframe
     
         A term originally referring to the cabinet
        containing the central processor unit or "main frame" of a
        room-filling {Stone Age} batch machine.  After the emergence
        of smaller "{minicomputer}" designs in the early 1970s, the
        traditional {big iron} machines were described as "mainframe
        computers" and eventually just as mainframes.  The term
        carries the connotation of a machine designed for batch rather
        than interactive use, though possibly with an interactive
        {time-sharing} operating system retrofitted onto it; it is
        especially used of machines built by {IBM}, {Unisys} and the
        other great {dinosaurs} surviving from computing's {Stone
        Age}.
     
        It has been common wisdom among hackers since the late 1980s
        that the mainframe architectural tradition is essentially dead
        (outside of the tiny market for {number crunching}
        {supercomputer}s (see {Cray})), having been swamped by the
        recent huge advances in {integrated circuit} technology and
        low-cost personal computing.  As of 1993, corporate America is
        just beginning to figure this out - the wave of failures,
        takeovers, and mergers among traditional mainframe makers have
        certainly provided sufficient omens (see {dinosaurs mating}).
     
        Supporters claim that mainframes still house 90% of the data
        major businesses rely on for mission-critical applications,
        attributing this to their superior performance, reliability,
        scalability, and security compared to microprocessors.
     
        [{Jargon File}]
     
        (1996-07-22)