mainframe: n. Term originally referring to the cabinet containing the central processor unit or `main frame' of a room-filling {Stone Age} batch machine.

:mainframe: n. 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 timesharing operating
system retrofitted onto it; it is especially used of machines built
by IBM, Unisys, and the other great {dinosaur}s 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} supercomputers (see
{cray})), having been swamped by the recent huge advances in IC
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}).
-- The AI Hackers Dictionary