mode bit

	This is the JargonFile ^(V4.00) entry for mode bit - Next: modulo, Prev: mode
:mode bit: /n./ 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.
* (text is auto-included via JargonExtension by mutante using jargon with VERSION 4.0.0, 24 JUL 1996* - JargonFile by Eric S. Raymond is in the public domain)*