Software Functional Overview 3-25
S3 – Sleeping State
The S3 sleeping state is a low wake-up latency sleeping state where all system
context is lost except system memory. CPU, cache, and chip set context are lost
in this state. Hardware maintains memory context and restores some CPU and
L2 configuration context. Control starts from the processor's reset vector after
the wake-up event.
S4 – Sleeping State
The S4 sleeping state has the lowest power and the longest wake-up latency
sleeping state supported by ACPI. In order to reduce the power to a minimum, it
is assumed that the hardware platform has powered off all devices. All platform
context is saved to disk.
S5 – Soft Off State
The S5 state is similar to the S4 state except the OS does not save any context
nor enable any devices to wake the system. The system is in the Soft Off state
and requires a complete boot when awakened. To distinguish whether or not the
boot is going to wake from a saved memory image, and allow for initial boot
operations within the BIOS, a different state value is used to depict between the
S5 state and the S4 state.
Power States
The following diagram visually interprets the system’s power states.
System Power States
