Power Supplies - Upgrading and Repairing PCs - page 917

The device states may or may not be visible to the user. For example, it may be obvious when a hard
disk has stopped or when the monitor is off; however, it may not be obvious that a modem or other
device has been shut down. The Device Power states are somewhat generic; many devices do not
have all four Power states defined.
Within the G1 Global Sleep state are four Sleep states (S1-S4). The G2 Global Soft Off state is also
known as the S5 Sleep state , in which case the system is powered off but still has standby power.
Finally, G3 is the Mechanical Off state, where all power is disconnected from the system.
The following list shows the definitions and nested relationship of the various Global, CPU/Device
Power, and Sleep states:
• G0 Working —This is the normal working state in which the system is running and fully
operational. Within this state, the Processor and Device Power states apply. The Device Power
states are defined as follows:
• G0/D0 Fully-On —The device is fully active.
• G0/D1 —Depends on the device; uses less power than D0.
• G0/D2 —Depends on the device; uses less power than D1.
• G0/D3 Off —The device is powered off (except for wakeup logic).
• The Processor Power states are defined as follows:
• G0/C0 CPU On —Normal processor operation.
• G0/C1 CPU Halted —The processor is halted.
• G0/C2 CPU Stopped —The clock has been stopped.
• 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, system 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 —A low-latency idle state. The CPU is halted; however, system context 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/S3 Suspend to RAM —All system context is lost except memory. The hardware
maintains memory context. The CPU is reset and restores some CPU and L2 context upon
wakeup.
• G1/S4 Suspend to Disk (Hibernation) —The system context and status (RAM contents)
have been saved to nonvolatile storage—usually the hard disk. This is also 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 Shutdown or