Allows one to modify the internal configuration registers in the 5x86 and 6x86 cpu. these include specifying non-cacheable memory areas (important for e.g. graphics cards), i/o delays, cache write policy (wb/wt), write-gathering, and also enable an automatic standby mode where a cpu "halt" instruction cuts down power by a factor of 70 (from 20 watts to 0.3 watts for the 6x86 p133+) when the cpu is idle. especially the cpu power reduction cuts down on most temperature-related problems on many motherboards.