mode bitA flag, usually in hardware, that selects between two (usually quite different) modes of operation. The connotations are different from flag bit in that mode bits are mainly written during a boot or set-up phase, are seldom explicitly read, and seldom change over the lifetime of an ordinary program. The classic example was the EBCDIC-vs.-ASCII bit (#12) of the Program Status Word of the IBM 360. Another was the bit on a PDP-12 that controlled whether it ran the PDP-8 or the LINC instruction set. [Jargon File]
modam ♦ MODCAL ♦ Mode ♦ mode ♦ mode bit ♦ MODEF ♦ MODEL ♦ model ♦ model checking
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