Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 358 — #384

Unlike APM, which was previously used on laptops for power manage-

ment only, the hardware information and conﬁguration tool ACPI is avail-

able on all modern computers (laptops, desktops, and servers). On many

types of modern hardware, the CPU frequency can be adapted to the situ-

ation, which helps save valuable battery time especially on mobile devices

(CPU frequency scaling).

All power management technologies require suitable hardware and BIOS

routines. Most laptops and many modern desktops and servers meet these

requirements. APM had been used in many older computers. As APM

largely consists of a function set implemented in the BIOS, the level of

APM support may vary depending on the hardware. This is even more true

of ACPI, which is even more complex. For this reason, it is virtually impos-

sible to recommend one over the other. Simply test the various procedures

on your hardware then select the technology that is best supported.

Note

Power Management for AMD64 Processors

AMD64 processors with a 64-bit kernel only support ACPI.

Note

17.1 Power Saving Functions

Although many of these functions are of general interest, they are espe-

cially important for mobile deployment. The following paragraphs describe

the functions and which systems offer them.

Standby This operating mode merely turns off the display. On some com-

puters, the processor performance is throttled. This function is not

available in all APM implementations. The corresponding ACPI state

is S1.

Suspend (to memory) This mode writes the entire system state to the

RAM. Subsequently, the entire system except the RAM is put to sleep.

As the computer consumes very little power in this state, the battery

may last anywhere from twelve hours to several days, depending

on the device. The advantage of this state is the possibility to resume

work at the same point within a few seconds without having to boot

and restart applications. Most modern devices can be suspended by

closing the lid and activated by opening it. The corresponding ACPI

state is S3. Support of this state largely depends on the hardware.

358 17.1. Power Saving Functions