The PC power question boils down to wearing out components by leaving the system on versus jolting the system with electricity through frequent on and off cycles.

The biggest stress on any electrical system is turning it on. Bruce Drenning, network engineer for DPSC Technology Consultants, says turning on any electrical appliance produces an initial electrical spike that is generally three times higher than the amount of electricity needed to power the appliance. You've witnessed this phenomenon if the lights in your home ever dimmed when you turned on a hair dryer. Light bulbs tend to blow with that initial spike of electricity produced when you turn them on. The more frequently you flip the switch on and off, the shorter the bulb's life. Leaving it on all the time protects the bulb from that spike, but it will still eventually burn out. The same is true of your PC, which tends to be particularly sensitive to that initial electrical spike.

Thermal stress is another startup problem for your PC and another good reason to leave it on. When the PC comes on, the components heat up and expand. When turned off, they cool down and contract. This cycle of thermal stress is more detrimental to the life span of your PC and is more of an immediate threat than the individual components wearing out.

Another school of thought says that the parts wear out anyway, so there is no reason to waste electricity by leaving your PC on all the time. Steven Koch, technical services engineer with Sony, advises keeping damage from the initial power surge in perspective. Jostling your computer in a move, smoking around it, and dropping it are all far more damaging than turning it off and on, he says.

Monitoring Power.

While there's no general consensus on PCs, manufacturers and technical support people say if you plan to leave your monitor for more than two hours, you should turn it off or put it in sleep mode. This special setting leaves the monitor on in a low-power mode. Newer operating systems let you program how long your monitor can be left unattended before "going to sleep."

A monitor running at full power consumes nearly as much power as a PC, which can significantly increase your electric bill. Figures vary considerably, but monitors in use can consume 80 to 150 watts. Most monitors we checked drew 8 to 15 watts in sleep mode. Turning off the monitor doesn't necessarily stop the drawing of power altogether. Any appliance with a memory setting and no battery backup will continue to draw 3 to 8 watts even when turned off. Monitors that let you set the screen width, for example, will preserve that setting when they're off, but to do it they need power. Without this feature, you have to reset the monitor each time you turn it on. Koch says the amount of power monitors draw is such a concern in the industry that Sony is working on a monitor with a zero-watt switch. The monitor draws close to zero watts and is as close to unplugging it as you can get without actually pulling the plug.

Power-saving features similar to these are a key feature in green PCs. The housing and internal components of these PCs are built with recyclable materials. Features such as low-energy sleep modes let green PCs run constantly with a negligible effect on electric bills.

Smart monitors, which meet the guidelines set by the Video/Electronic Standards Association (VESA), have four stages in which the monitor gradually uses less power. These monitors can be programmed through operating systems that comply with Display Power Management Signaling (DPMS) standards. The first DPMS stage is on and functioning—either the monitor is in use or the screen saver is engaged. In this stage, the monitor draws peak power. In the standby stage, the monitor draws 50% less power and offers a fast reaction to input; it responds almost immediately to mouse movement. In the suspend (or sleep) stage, the picture tube is actually off, and the monitor draws 10 to 15 watts. To get out of suspend, you must press the PC's wake-up or sleep button. Because the picture tube was off, the monitor will slowly grow brighter just as it does when you first power up for the day. The final stage is off, but the monitor has not been physically switched off by the user. The circuitry is still active, and the monitor is drawing 3 to 7 watts. Newer Windows-based operating systems offer the configurations that determine how much time elapses before the monitor gradually powers down.

If your monitor lacks the power-down features outlined above, the easiest way to prolong its life is to turn it off each day. Monitors are subject to thermal stress, but the life span of a monitor is inversely related to the amount of time it is on. The longer it's on, the shorter its life span. Young Bae, product manager for CTX International, says monitors are far less sensitive to the power spike than PCs, and the secret to monitor longevity is turning it off daily.

You should also turn your monitor off or put it in sleep mode because phosphor, the chemical lining in the tube in your monitor, has a limited life. When the screen is on, the phosphor glows to produce the on-screen image. Years ago a static image on the screen would burn itself permanently into the phosphor, producing persistent "ghost" images. Monitor makers warned us to keep the images moving on the screen or shut off the monitor. Although burn-in technically is still possible, Koch laughingly says that the image would have to be on your screen for about 12 years before burning in! Monitors have a finite amount of phosphor, however, and as the monitor ages, the phosphor grows dimmer and dimmer. You will enhance the life of the phosphor significantly by putting the monitor in sleep mode, using a darkened screen saver, or turning the monitor off when it is not in use.

Which Comes First?

If you turn off your PC, monitor, and other hardware such as printers and scanners every day, several monitor manufacturers suggest turning on the monitor first when you restart everything. Bae explains that the PC's operating system will query the monitor about its identity, and it's possible that the operating system won't interface properly with the monitor if it can't find it during the initial search. That is a rare problem, but you can avoid the possibility by turning on your monitor first. Koch says one Sony system specifically requires that the computer be turned on first, but with most systems, you may turn on the monitor first.

Many users want to power up and power down their PCs and related hardware with a single switch. Manufacturers and technicians we interviewed agreed that shutting off the entire configuration at the power strip isn't a problem—as long as you follow the shutdown procedure for your operating system.

Operating System.

That software step is a critical one for any system shutdown. Failing to shut down the operating system can damage files and produce a long delay when you turn on your PC again. The wait will be similar to the delay experienced when you restart the PC after an abrupt loss of power, which is essentially what your operating system suffers when shut down improperly. To do things right, click the Start button in Windows 95 and choose Shut Down. In Windows 3.1, choose Exit Windows from Program Manager's File menu.

Even if you regularly put your computer to sleep or leave it on, Drenning advises shutting down and restarting the operating system regularly. The longer you go without rebooting (restarting), the more likely a crash becomes. Your PC regularly creates temporary files while running. These files are normally discarded when you shut down the operating system, but if you never reboot, the temporary files get huge, and the entire system will run sluggishly. Drenning advises performing a warm reboot once a day, and, at minimum, once every three days to clear the cache (memory that stores frequently used data) and regular memory. A warm reboot occurs when you push the Reset button on the PC's case or restart the operating system without shutting off the PC. A cold reboot involves physically turning off the PC.

Another kind of software shutdown is important for PCs connected to a network. Network users probably log out at the end of each day, if not turn off the system entirely. Dr. Mark Misic, director of information systems & communication services for the College of Business at Northern Illinois University, says server software (which runs a network) cannot be upgraded when individual users are online and using it. Just think of the problems that could arise if you tried upgrading software on your PC while using the application.

Individuals who leave applications open during a network hardware change cause problems for the server itself. Before a network hardware change, a complete backup of everything on the server is necessary. If individual users have files open at the time of the backup, it's possible that the server won't read or back up the open file, or the server may simply hang up at that point.

The choices for network users are obviously more restrictive than those for users of single PCs. On your desk, the only real shutdown requirement is to regularly restart the operating system to avoid crashes and sluggish performance. You have the power to make your own policy on the other power questions.

by Katie Powers