AutoHALT state or AutoHalt Power Down state is a low-power state
supported by majority of modern x86 microprocessors. To switch to
this state the operating system executes HALT instruction. When in
this state, the CPU has internal clock running and may respond to
interrupts and other signals. The CPU may transition from AutoHalt
state to Normal state, Stop Grant
low-power state and for some micro-architectures to other
low-power states. Power savings in this mode can be significant -
from 50% for Pentium 4 Northwood and higher for other processors.
Please note that although processor's clock is not stopped in this
mode, the CPU effectively is not running, i.e. not executing any
instructions.
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