1E 2009

 

Page 4 of 16

 

Introduction

Power management of some sort has been included as part of the operating system since portable computing first

started relying on batteries as an energy source.

The recent rises in the cost of energy coupled with the growing awareness of the environmental impact of

unnecessary energy use has increased the requirement for Power Management on all PCs, not just portable ones.

There are now many 3

rd

 party PC Power Management solutions available in the marketplace, which suggests that

the built-in power management capabilities of the operating system must be lacking in some way, otherwise there

would be no market into which to sell these products.

This document examines where the limitations of the built-in power management solutions lie and how

NightWatchman addresses them.

Data was collected from over three thousand PCs, initially without enforcing any NightWatchman power policies.

This enabled analysis of the behavior of end users when left to decide how to configure their PCs power

management settings, and the effectiveness of relying on Windows power scheme sleep timers to save energy. This

was then compared to the behavior when NightWatchman power policies had been set to perform a nightly

scheduled power down.

Power Management

The energy usage of a PC is dependent on several things:

"   The make and model of the PC, and the components used in its construction. 

"   The utilization of PC resources (CPU, Memory, Disk etc.)   the busier a PC is the more energy it consumes. 

"   The power state of the Monitor   a monitor uses a lot less energy when it goes into a standby state. Monitors 

can be switched into and out of standby within a very short time (1-2 seconds) without adversely impacting

user productivity.

"   The power state of the PC   a PC that is powered down uses a lot less energy than one that is powered up. 

There are several different ways in which the energy use of a PC can be managed.

Idle Timers 

The standard paradigm for built-in power management is to use idle timers. A set of timers specify the periods of

time after a user has stopped using the PC when a power related event will occur. The standard set of events

covered by most operating system built-in functionality includes:

"   Placing the monitor into a standby state 

"   Spinning down the hard disk 

"   Placing the PC into a low power state (also known as powered down), equivalent to ACPI system states S3 

(known as Sleep or Standby), S4 (known as Suspend or Hibernate) and S5 (known as Shut Down, Switched

Off or Powered Off).