PCs aren't the most power-hungry devices in your home or office, but they do typically draw between 45 and 200 watts of power, plus 80 to 120 watts for the monitor.
Just how much power they draw depends mostly on how the machine is configured and the speed of the CPU.
Even at today's higher rates, using a PC costs only pennies an hour. But during this energy crisis, every watt counts.
Short of pulling the plug on your PC, you can at least turn off the monitor or make sure you're taking advantage of all the energy-saving technology built into the machine.
You might have heard that it's better to leave machines running all the time rather than turn them off when you're not using them. That may have been true in the days of vacuum tubes, but it's not true now.
Today's computers and other electronics are mostly solid-state, and there is virtually no harm done when you turn them on and off.
Screen-saver programs, which put images on your screen while you're away from the PC, can be fun, but they don't save energy. In fact, they waste energy by lighting up the monitor, taxing memory and the CPU. A better solution would be to turn off the monitor or, if possible, take advantage of the machine's ability to put the monitor into sleep mode when not in use.
Today's machines are supposed to go into some type of sleep mode automatically after a specified period of inactivity. That's part of the Environmental Protection Agency's Energy Star (http://www.energystar.gov) certification requirements agreed to by virtually all major PC makers.
Depending on your machine and operating system, you may have two types of sleep mode: standby and hibernation.
In standby mode, the "state" of the machine (programs that are running and data in memory) is copied into an area of the PC's memory that stays alive while the machine is standing by.
The hard drive, monitor and other components are turned off, but a very small amount of power is used to keep the memory alive so that it can store the data it needs when the machine wakes up.
Though it sometimes works as advertised, I've used several desktop and laptop machines that fail to wake up from standby mode, which is available on Windows 98, Windows ME and Windows 2000.
According to engineers I've spoken with at Compaq, IBM and Microsoft, problems can occur if any of the peripherals or accessories on your machine are noncompliant or simply not functioning properly.
Engineers from these companies, along with a spokesperson from the EPA, told me that things should get better fairly soon thanks to new power-management specifications, including the Instantly Available PC, or IAPC, technology from Intel. According to the EPA, it will enable "a PC to power down to a sleep mode when not in use and quickly awaken in seconds."
Hibernation mode, which is not available on some older machines, is similar to standby but with one important difference: Instead of writing the state of the machine into memory, it copies it to your hard drive and then shuts the machine off completely.
A machine is more likely to come out of hibernation than standby, and data won't be lost in the event of a power failure or rolling blackout. The only downside is that it takes a bit longer to put your machine in and out of hibernation because you have to wait for data to be transferred to and from the hard drive. Still, it's a lot faster than a standard shutdown and start-up.
To set power management in Windows, go to the Settings menu, select Control Panel and click on Power Options. Depending on your machine, you might or might not see a tab for hibernation. If you do, that's your best option. Otherwise, experiment with the standby options.
If your machine goes to sleep and wakes up properly, then you're in good shape. If not, turn off the energy-saving features and visit your PC manufacturer's Web site or call tech support to see whether there are any software updates that might improve power management.
Technology reports by Lawrence J. Magid can be heard between 2 and 3 p.m. weekdays on the KNX-AM (1070) Technology Hour.