PC power management
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PC power management refers to the mechanism for controlling the power use of personal computer hardware. This is typically through the use of software that puts the hardware into the lowest power demand state available. It is an aspect of Green computing.
A typical office PC might use on the order of 90 watts when active (approximately 50 watts for the base unit, and 40 watts for a typical LCD screen); and three to four watts when ‘asleep’. Up to 10% of a modern office’s electricity demand might be due to PCs and monitors.
While some PCs allow low power settings, there are many situations, especially in a networked environment, where processes running on the computer will prevent the low power settings from taking effect. This can have a dramatic effect on energy use that is invisible to the user. The monitor may have gone into standby mode, and the PC may appear to be idle, but operational testing has shown that on any given day an average of over 50% of an organisation's computers would fail to go to sleep, and over time this happened to over 90% of the machines.
Windows 'Insomnia' (Sleepless PCs)
The Windows power management system is based upon an idle timer. If the computer is idle for longer than the preset timeout then the PC may be configured to sleep or hibernate. The user may configure the timeout using the Control Panel. Windows uses a combination of user activity and CPU activity to determine when the computer is idle.
Applications can temporarily inhibit this timer by using the SetThreadExecutionState API. There are legitimate reasons why this may be necessary such as burning a DVD or playing a video. However, in many cases applications can unnecessarily prevent power management from working. This is commonly known as Windows 'Insomnia' and can be a significant barrier to successfully implementing power management.
Common causes of 'insomnia' include:
- Legacy or non-power management aware applications
- Open file handles on remote computers
- Faulty mice which can cause pointer drift. This makes the operating system believe that a user is present
- Scheduled maintenance tasks causing significant CPU activity
- High network activity
Operating systems have built-in settings to control power use. Microsoft Windows supports predefined power plans and custom sleep and hibernation settings through a Control Panel Power Options applet. Apple's OS X includes idle and sleep configuration settings through the Energy Saver System Preferences applet. Likewise, Linux distributions include a variety of power management settings and tools.
There is a significant market in third-party PC power management software offering features beyond those present in the Windows operating system. Products are targeted at enterprise environments offering Active Directory integration and per-user/per-machine settings with the more advanced offering multiple power plans, scheduled power plans, anti-insomnia features and enterprise power usage reporting. Notable vendors include 1E NightWatchman, Data Synergy PowerMAN (Software), Faronics Power Save, Verdiem SURVEYOR. and EnviProt Auto Shutdown Manager
Using this type of energy management tool on an organisation's network has been demonstrated to save on average 200 kg of CO2 emissions per PC per year, and generate $36 per PC per year in energy savings. An organisation such as a large office, with 4,000 employees, would be able to make CO2 emissions savings of over 800 tonnes and about $140,000 per year in energy savings. A large corporation with 50,000 employees could save 10,000 tonnes of CO2 and about $1.7 million per year in energy costs.
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