Computer power management
- Research shows that personal computers (PC) are not being actively used during the vast majority of the time that they are kept on. It is estimated that an average PC is in use 4 hours each work day and idle for another 5.5 hours.
- It's also estimated that some 30-40 percent of the US's work PCs are left running at night and on weekends.
 When to turn off personal computers
If you're wondering when you should turn off your personal computer for energy savings, here are some general guidelines to help you make that decision.
Though there is a small surge in energy when a computer starts up, this small amount of energy is less than the energy used when a computer is running for long periods of time. For energy savings and convenience, consider turning off:
- the monitor if you aren't going to use your PC for more than 20 minutes
- both the CPU and monitor if you're not going to use your PC for more than 2 hours.
Make sure your monitors, printers, and other accessories are on a power strip/surge protector. When this equipment is not in use for extended periods, turn off the switch on the power strip to prevent them from drawing power even when shut off. If you don't use a power strip, unplug extra equipment when it's not in use.
 Will it harm my PC?
It's a myth that turning computers off and on shortens their lives -- unless you turn them off many, many, many times every day. It's also a myth that starting the computer requires a lot of "extra energy": it actually only takes the equivalent of a few seconds of running time power.
Most PCs reach the end of their "useful" life due to advances in technology long before the effects of being switched on and off multiple times have a negative impact on their service life. The less time a PC is on, the longer it will "last."
Computers generate a lot of heat -- principally from their central processor units (CPU). Allowing a "cool down" during a power-off period will generally increase the life span of the entire system. Allowing your computer to rest its moving parts, like the spinning hard drive, cooling fans, etc., will tend to increase the life-span of those components.
The reboot of the system that takes place when power is restored has another positive effect. Many software patches and upgrades require a reboot to be fully installed and functional. A computer that is only rarely rebooted may lag behind on software updates, and accordingly be more vulnerable to malware attacks.
 Power-Down or Sleep Mode Features
Many PCs available today come with a power-down or sleep mode feature for the CPU and monitor. ENERGY STAR computers power down to a sleep mode that consume 15 Watts or less power, which is around 70% less electricity than a computer without power management features. ENERGY STAR monitors have the capability to power down into two successive "sleep" modes. In the first, the monitor energy consumption is less than or equal to 15 Watts, and in the second, power consumption reduces to 8 Watts, which is less than 10% of its operating power consumption.
Make sure you have the power-down feature set up on your PC through your operating system software. This has to be done by you, otherwise the PC will not power down. If your PC and monitor do not have power-down features, and even if they do, follow the guidelines below about when to turn the CPU and monitor off.
Note: Screen savers are not energy savers. Using a screen saver may in fact use more energy than not using one, and the power-down feature may not work if you have a screen saver activated. In fact, modern color monitors do not need screen savers at all.
- See this guide to Saving power on idle PCs
- Also see: devices on standby
 Power-Down Software
Windows XP makes it very hard to centrally configure power management features. Microsoft have improved this in Windows Vista but due to the high proportion of the older operating system still deployed it has failed to make much impact. There are several software products available that help IT administrators resolve this problem. The better products include a feedback or reporting system to ensure everything is working correctly.
There is also a freeware program called Granola for individuals using a computer running Linux or Windows made in the past five years. Granola reduces the power consumption of the processor by intelligently slowing it down during periods of idle or light use and adjusting performance on the fly so that the user doesn't notice any performance loss. Users who install this program on laptops also notice increased battery uptime as a result of the decreased energy consumption.
- For a guide to power consumption of different types of computer go to: www.complang.tuwien.ac.at -computer power consumption