A 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]

In addition suitable contents:
[ 2 ] [ = ] [ ad ] [ ag ] [ ai ] [ al ] [ am ] [ an ] [ ar ] [ arc ] [ arg ] [ AS ] [ as ] [ ASCII ] [ at ] [ B ] [ b ] [ BC ] [ BCD ] [ be ] [ bi ] [ bit ] [ bo ] [ boot ] [ C ] [ CD ] [ ch ] [ ci ] [ cl ] [ class ] [ classic ] [ co ] [ con ] [ control ] [ D ] [ de ] [ diff ] [ do ] [ DP ] [ du ] [ E ] [ EBCDIC ] [ ec ] [ ed ] [ ee ] [ er ] [ era ] [ es ] [ et ] [ fi ] [ file ] [ flag ] [ fr ] [ ge ] [ gr ] [ h ] [ hang ] [ hardware ] [ hat ] [ hr ] [ IBM ] [ IBM 360 ] [ IC ] [ id ] [ iff ] [ il ] [ in ] [ instruction set ] [ io ] [ it ] [ J ] [ Jargon File ] [ la ] [ lag ] [ ld ] [ Lex ] [ li ] [ life ] [ ly ] [ M ] [ ma ] [ mo ] [ mod ] [ mode ] [ module ] [ mp ] [ N ] [ na ] [ NC ] [ ng ] [ nl ] [ nn ] [ no ] [ ns ] [ om ] [ op ] [ PD ] [ PDP ] [ pe ] [ ph ] [ phase ] [ pl ] [ pr ] [ program ] [ query ] [ rc ] [ re ] [ ro ] [ ru ] [ S ] [ SC ] [ SCI ] [ se ] [ set ] [ si ] [ st ] [ struct ] [ su ] [ T ] [ th ] [ tr ] [ troll ] [ tt ] [ tw ] [ ua ] [ up ] [ us ] [ ve ] [ Word ]