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Marshall

Hi, I’m Marshall Brain with today’s question.

Why Does Your Computer Need A Battery?

Most computers have a small battery, about the size of a nickel. The battery is usually in some sort of holder that sits on the motherboard, so it’s easy to replace. Computers are not the only things that have a small battery like this. Camcorders and digital cameras often have them as well. Just about any gadget that keeps track of time will have a little battery. In your computer as well as these other gadgets, the battery powers a chip called the real time clock chip. The real time clock is essentially a quartz watch that runs all the time, whether or not the computer has power. The battery powers this clock.

When the computer boots up, part of the process is to query the real time clock chip to get the correct time, and date. A little quartz clock like this might run for 5 to 7 years off that small battery. Then it is time to replace the battery. In many cases, once the battery fails, your computer will no longer boot up. You would expect the computer to boot fine, but have an incorrect time and date. The reason your computer will not boot is because the real time clock chip also contains 64 or more bytes of random access memory, known as the CMOS RAM. The clock uses 10 bytes of this space, leaving 54 bytes for other purposes. The BIOS stores all sorts of information in CMOS RAM area, like the number of drives, the hard disk drive type, and stuff like that. If the CMOS RAM loses power, the computer may not know anything about the hard disk configuration on your machine, and therefore it cannot boot.

More modern computers are not quite so dependent on the CMOS RAM. They store their settings in non-volatile RAM that works without any power at all. If the battery goes dead, the clock fails, but the computer can still boot using the information in this non-volatile RAM area. Then, once the computer can see the network it can query a time-server from the network, and set the clock that way.

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