by Jeff Smith
Every computer (that I've ever seen anyway) has a small battery that is usually located on the motherboard. The purpose of this battery is to keep a small amount of electrical current supplied to the BIOS chip and the system clock. This allows the computer to save your BIOS settings and keep your system clock up to date even though your machine may have been banished to the back of the garage or closet for months on end. Its basically a watch-battery, roughly the size and shape of a nickel, and you can get a replacement pretty easily at Walmart or K-Mart or RadioShack. They usually cost around $5 or less.
They are usually pretty easy to replace, given that they are most often held in by a simple clip, in fact the most difficult part of the process is often just getting to it. Its a good idea to go into your BIOS and write down all of the settings BEFORE it goes bad.
CMOS stands for Complementary Metal Oxide Semiconductor, and it doesn't really have anything to do with the battery, but with the type of computer chips that the battery is providing power to.
WHEN SHOULD I CHANGE IT?
When your CMOS battery goes dead you'll often experience messages during boot time that your BIOS settings are being "reset to default" and your clock will reset to a few years ago. Clocks on older machines may reset back to 1981! When you begin to experience these signs, its a good indication that you should change your battery.
Default settings often don't take full advantage of your hardware, so if your settings get reset, it could result in a loss of performance.
They usually last for years, so if you have a new computer, you're not likely to have to deal with this for a while. Keep in mind that replacing the battery will also wipe out your settings, so be sure to write down your settings before replacing it.
Thats it for this week, see you next time!