Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 359 — #385
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17
Power Management
Hibernation (suspend to disk) This operating mode enables the com-
puter to hibernate, as the entire system state is written to the hard
disk and the system is powered off. The reactivation from the state
of hibernation takes about thirty to ninety seconds. The state prior
to the suspend will be restored. Some manufacturers offer useful
hybrid variants of this mode in their APM (such as RediSafe in IBM
Thinkpads). The corresponding ACPI state is S4.
Battery monitor In addition to monitoring the battery charge level, some-
thing must be done when power reserves are low. This control func-
tion is handled by ACPI or APM.
Automatic power-off Following a shutdown, the computer is powered
off. This is especially important when an automatic shutdown is per-
formed shortly before the battery is empty.
Shutdown of system components The most important component for
saving power is the hard disk. Depending on the reliability of the
overall system, the hard disk can be put to sleep for some time. How-
ever, the risk of losing data increases with the duration of the sleep
periods. Other components can be deactivated via ACPI (at least the-
oretically) or permanently in the BIOS setup.
Processor speed control AMD PowerNow! and Intel SpeedStep are two
concepts designed for reducing the power consumption of the overall
system. For this purpose, the power consumption of the most power-
hungry component — the processor — is reduced. A pleasant side-
effect of the reduced processor speed is the reduced generation of
heat. Thus, adjustable fans will also make less noise. This feature is
controlled by the CPU frequency scaling functions of the Linux ker-
nel. Basically, three different processor speed levels are available:
performance Maximum processor performance for AC operation.
powersave Minimum processor performance for battery operation.
dynamic Dynamic adaption of the processor performance to the cur-
rent processor load — this is the recommended setting for bat-
tery operation and AC operation to save battery power, reduce
noise, and achieve optimum performance. Switching between
the speed levels usually takes place seamlessly, unnoticed by the
user.
See Section 17.5 on page 369 for more information about controlling
the processor speed.
359SUSE LINUX Enterprise Server