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Sleeping States (S-States)

Sleeping states define the computer's ‘sleeping methods’ in the G1 (sleeping) state. In all the sleeping states (except S0 and S5),

  1. The CPU executes no instructions. It is having a good sleep!
  2. User applications will not run (duh… the CPU is sleeping!)
  3. Some devices sleep partially because they need to generate wake up events.
  4. When the system is ‘awakened’, it will continue working from the point before it slept.

S1 State

  • The hardware maintains all its system context.
  • The CPU input clock will be stopped, and its caches will be invalidated.
  • The system memory goes into its self-refreshing mode.
  • All system clocks are turned off, except the real time clock.
  • Power consumption is much lower than G0 working state.
  • Wake up latency is low. It takes about 2 seconds to go back to the G0 working state. The hardware will be responsible for restarting the system clocks.
  • Example : “Stand-by” mode in Windows XP, if the S3 state isn’t supported.

S2 State

  • Similar to S1 state - the only difference is the CPU power state.
  • In S2, the CPU and its caches are powered down, instead of just gating the clock input and invalidating the caches.
  • The S2 wake up latency is slightly longer than S1, but it saves slightly more power.

S3 State

  • The S3 state powers down the CPU, cache, chipset and peripherals, except RAM.
  • Some devices necessary to maintain memory context will still run.
  • RAM goes into a low-power, self-refreshing mode.
  • The power consumption is as low as the power requirement of the RAM (at idle power), plus some necessary onboard devices only.
  • The wake-up latency is about 5-6 seconds.
  • Example : "Stand-by" mode in Windows XP if the S3 state is supported by hardware.

S4 State

  • All devices including system RAM are powered down.
  • Only platform settings are maintained, while other settings are stored in a special partition in the hard drive.
  • When successfully switched into the S4 state, the system appears to be turned off to the user.
  • The power consumption is very low (< 3W), as almost everything has turned off.
  • We need to go through the BIOS boot sequence again when the computer is awakened.
  • The OS reboot is not required. It will automatically return to where you last left it.
  • Example : "Hibernate" mode in Windows XP

 

Sleeping States Summary

Sleep State
Wake Up
Latency
Power
Consumption
BIOS
Reboot
OS
Reboot
CPU
Cache
Chipset
RAM
S0 (G0)
none
large
no
no
on
on
on
on
S1 (G1)
2-3s
medium
no
no
no clock
invalidated
no clock
self refresh
S2 (G1)
3-4s
mid-low
no
no
off
off
no clock
self refresh
S3 (G1)
5-6s
low
no
no
off
off
off
low power
self refresh
S4 (G1)
20-30s
very low
yes
no
off
off
off
off
S5 (G2)
> 30s
near zero
yes
yes
off
off
off
off


<<< Global System States (G-States), Global States Summary : Previous Page   |   Next Page : Device States (D-States), D-State Examples >>>

 

 
   
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