Hardware Reference
In-Depth Information
•
G0/C3 CPU/Cache Stopped
—The clock has been stopped and cache snoops are
ignored.
•
G1 Sleeping
—The system appears to be off but is actually in one of four Sleep
states—up to full hibernation. How quickly the system can return to G0 depends on
which of the Sleep states the system has selected. In any of these Sleep states, sys-
tem context and status are saved such that they can be fully restored. The Sleep states
available in the Global G1 state are defined as follows:
•
G1/S1 Halt
—Alow-latencyidlestate.TheCPUishalted;however,systemcontext
and status are fully retained.
•
G1/S2 Halt-Reset
—Similar to the S1 sleeping state except that the CPU and cache
context is lost, and the CPU is reset upon wakeup.
•
G1/S3SuspendtoRAM
—Allsystemcontextislostexceptmemory.Thehardware
maintainsmemorycontext.TheCPUisresetandrestoressomeCPUandL2context
upon wakeup.
•
G1/S4 Suspend to Disk (Hibernation)
—The system context and status (RAM
contents)havebeensavedtononvolatilestorage—usuallytheharddisk.Thisisalso
known as
Hibernation
. To return to G0 (Working) state, you must press the power
button, and the system will restart, loading the saved context and status from where
they were previously saved (normally the hard disk). Returning from G2/S5 to G0
requires a considerable amount of latency (time).
•
G2/S5 Soft Off
—This is the normal power-off state that occurs after you select Shut-
down or press the power button to turn the system off. The system and all devices
are essentially powered off; however, the system is still plugged in and standby power
is coming from the power supply to the motherboard, allowing the system to wake
up (power on) if commanded by an external device. No hardware context or status is
saved. The system must be fully rebooted to return to the G0 (working) state.
•
G3 Mechanical Off
—Power is completely removed from the system. In most cases
this means the system must be unplugged or the power turned off via a power strip.
This is the only state in which it is safe to disassemble the system. Except for the
CMOS/clock circuitry, power consumption is completely zero.
In normal use, a system alternates between the G0 (Working) and G1 (Sleeping) states.
In the G1 (Working) state, individual devices and processors can be power-managed via
the Device Power (D1-D3) and Processor Power (C1-C3) states. Any device that is se-
lectively turned off can be quickly powered on in a short amount of time, from virtually
instantaneous to only a few seconds (such as a hard disk spinning up).
