mode bit

mode bit

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.
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Consumer Stalls focused on Comparison Board of Incandescent Bulb and CFL, Practical Demonstration of Standby Mode bites Energy.
Software selects these modes by setting one (and only one) of the three power-saving mode bits. The 603 provides a separate interrupt and interrupt vector for power management: the System Management Interrupt (SMI).
For example, as part of the OS loading/start-up process, one of the power-saving modes is selected by setting the appropriate power management mode bits. The proper power management mode is selected on the basis of whether any other devices will be performing DMA transfers that need to be snooped by the 603.