17.op/AJS.lorch
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Operating System Techniques for Reducing Energy Consumption
in Portable Computer Systems

Jacob R. Lorch

(Professor A. J. Smith)

NSF Graduate Fellowship

Computer systems have traditionally been designed with little regard
for energy consumption. Two factors, however, are leading to an
emphasis on minimizing power requirements. First, laptop computers
are becoming popular, and they are able to run for only short periods
of time with existing battery technology.
Second, federal and state
regulations, power and air conditioning costs, and noise from fans are
leading to pressure to decrease the power demands of office computers. Hardware exists to solve these power problems, but in many cases
it requires software intervention to achieve the best results.

Typically, hardware supports power reduction in that system components
have more than one state, with certain states being more functional
but less power-intensive than others. For example, the Kittyhawk
C3013A disk drive consumes 300 mA while spinning; its power
consumption can be reduced to 125 mA by allowing the motor to stop
spinning, at the expense of increased latency for the subsequent
operation. Other systems with low-power states are the CPU, the
display, and DRAM. The key to power management is deciding when to
switch components between such states.

We seek to devise strategies for making such transition decisions, and
also for minimizing their resultant penalties. Then, we plan to
obtain detailed traces of user activity, especially in a laptop
environment, to test the effectiveness of these strategies.