Making power management pay off

With rising energy costs and growing awareness of the environmental costs of
power production, companies of all sizes are increasingly interested in implementing
power management and today's PCs make it easier than ever to get work done in
a more energy-efficient manner. So why isn't everyone implementing power management?
Because understanding the available settings and standards is only half the
battle.

Organizations must also consider the role of power management in the organization
and how to implement it without inconveniencing end users. If a PC causes a
software conflict or other crash when it enters or exits a low-power state,
users and executives alike are apt to call for disabling power management altogether
rather than risk data or productivity losses. Likewise, if the cost of energy-efficient
PCs is greater than the money saved from increased efficiency, few enterprises
will buy them.

How power management works

The goal of power management is to use power efficiently -- to get the most work
done per unit of energy. Part of this depends on how much power the machine
uses to do a task. If one machine requires 100 watts to do one unit of work
and another machine uses 50 watts to do the same work, the second machine will,
all things being equal, use less power.

But, power management in the real world is more complicated. Computers don't
just go on and off -- instead, they (and their individual components) have various
levels of activity and idleness. Those levels, or "states," range
from unplugged (completely off) to "asleep" to actively working. To
be highly efficient, a computer should be able to switch as quickly as possible
between the lowest practical power setting and higher, more active settings.
And, it must make that switch without impairing the ability of the machine to
perform useful work. Power management that disrupts functionality is not useful.

Generally speaking, lower-power states have greater wake latency (they take
longer to "wake up") than higher-power states (the highest power state
being "awake and working"). Industry standards go to great lengths
to define specific power states for systems and system components. These are
mostly of use to manufacturers (for more information, read Advanced
Configuration and Power Interface Specifications).

From a practical standpoint, a few system states are typically readily available
to end users:

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