You wouldn't think to look at them, but PCs are picky eaters. They subsist on a diet of uninterrupted, precisely regulated electricity. Provide too little power, and your system behaves erratically or completely blacks out. Provide too much, and its tiny circuits--each 1/400th the width of a human hair, or thinner--are permanently fried. Here's how to ensure that your computer is properly nourished.

Safety First

The biggest threat to your PC's survival is a sudden increase--or spike--in the amount of electric current flowing to it. Normally, your PC's power supply controls the flow of electricity from the wall socket into the system. But a fallen power line or nearby lightning strike can easily overwhelm the power supply and send a mortal surge of electricity coursing through your motherboard.

Safeguard your computer with a high-quality surge protector. Expect to spend at least $20 to $30; cheaper models probably won't provide the shielding your machine needs. The surge protector should meet the Underwriters Laboratories' UL 1449 specification (most will state this on their packaging).

If your area is prone to electrical storms or other power fluctuations, get a surge protector with an indicator light to confirm that the unit is working properly. Many surge protectors lose their ability to guard against excess current after a single high-voltage surge. Since the unit still provides power to your PC, without an indicator light there's no way to know whether the device has lost its ability to fend off surges. Note that some surge protectors, such as Kensington's $40 SmartSockets tabletop unit, have an audible alarm to indicate when a surge has damaged the unit.

Don't forget your phone lines: Your modem and telephone are just as vulnerable to power spikes as your PC is. You can buy a phone-line protector separately or as a feature of your surge protector.

Providing too little voltage to your PC can be as bad as providing too much. A sudden absence of power can trash unsaved data or damage important system files, both of which can be devastating to a business. To avoid these pitfalls, install an uninterruptible power supply. When the power goes out, a UPS provides sufficient operating current to your PC (usually no more than 10 minutes' worth) for you to save your data and properly shut down the computer. UPSs often come with software that automatically does this for you if you're not around.

Many UPSs cost less than $100. American Power Conversion offers a wide selection of affordable power-protection products, including the $40 Back-UPS ES 350VA (see FIGURE 1).

But don't pinch pennies. A UPS must be able to meet your PC's power needs. Before buying, check the UPS's specifications for maximum running time and wattage values, and compare them with your PC's wattage requirements (see next page). And be wary: Some UPS vendors state the run time for a "half load," or half the wattage load listed in the specs. Rarely are all the components of a PC running at full speed concurrently, so a UPS vendor's claim to keep your PC running for x minutes is based on a PC's usual power load, not its rated maximum.

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