linux/Documentation/power/apm-acpi.txt
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   1APM or ACPI?
   2------------
   3If you have a relatively recent x86 mobile, desktop, or server system,
   4odds are it supports either Advanced Power Management (APM) or
   5Advanced Configuration and Power Interface (ACPI).  ACPI is the newer
   6of the two technologies and puts power management in the hands of the
   7operating system, allowing for more intelligent power management than
   8is possible with BIOS controlled APM.
   9
  10The best way to determine which, if either, your system supports is to
  11build a kernel with both ACPI and APM enabled (as of 2.3.x ACPI is
  12enabled by default).  If a working ACPI implementation is found, the
  13ACPI driver will override and disable APM, otherwise the APM driver
  14will be used.
  15
  16No, sorry, you cannot have both ACPI and APM enabled and running at
  17once.  Some people with broken ACPI or broken APM implementations
  18would like to use both to get a full set of working features, but you
  19simply cannot mix and match the two.  Only one power management
  20interface can be in control of the machine at once.  Think about it..
  21
  22User-space Daemons
  23------------------
  24Both APM and ACPI rely on user-space daemons, apmd and acpid
  25respectively, to be completely functional.  Obtain both of these
  26daemons from your Linux distribution or from the Internet (see below)
  27and be sure that they are started sometime in the system boot process.
  28Go ahead and start both.  If ACPI or APM is not available on your
  29system the associated daemon will exit gracefully.
  30
  31  apmd:   http://ftp.debian.org/pool/main/a/apmd/
  32  acpid:  http://acpid.sf.net/
  33
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