WEBVTT - Why does your computer need a battery?

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<v Speaker 1>Welcome to Brainstuff from house Stuff Works dot com where

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<v Speaker 1>smart happens. Hi am Marcia Brain with today's question, why

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<v Speaker 1>does your computer need a battery? Most computers have a

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<v Speaker 1>small battery about the size of a nickel. The battery

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<v Speaker 1>is usually in some sort of holder that sits on

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<v Speaker 1>the motherboard so it's easy to replace. Computers are not

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<v Speaker 1>the only things that have a small battery like this.

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<v Speaker 1>Camcorders and digital cameras often have them as well. Just

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<v Speaker 1>about any gadget that keeps track of time. We'll have

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<v Speaker 1>a little battery in your computer as well as these

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<v Speaker 1>other gadgets. The battery powers a chip called the real

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<v Speaker 1>time clock chip. The real time clock is essentially a

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<v Speaker 1>courtz watch that runs all the time whether or not

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<v Speaker 1>the computer has power. The battery powers this clock. When

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<v Speaker 1>the computer boots up, part of the process is to

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<v Speaker 1>query the real time clock chip to get the correct

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<v Speaker 1>time and date. A little quartz clock like this might

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<v Speaker 1>run for five to seven years off that small battery.

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<v Speaker 1>Then it's time to replace the battery. In many cases,

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<v Speaker 1>once the battery fails, your computer will no longer boot up.

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<v Speaker 1>You would expect the computer to boot fine, but have

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<v Speaker 1>an incorrect time and date. The reason your computer will

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<v Speaker 1>not boot is because the real time clock chip also

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<v Speaker 1>contains sixty four or more bytes of random access memory

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<v Speaker 1>known as the se Moss RAM. The clock uses ten

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<v Speaker 1>bytes of this space, leaving fifty four bytes for other purposes.

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<v Speaker 1>The bios stores all sorts of information in the sims

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<v Speaker 1>RAM area, like the number of drives, the hard disc

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<v Speaker 1>drive type, and stuff like that. If the sms RAM

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<v Speaker 1>loses power, the computer may not know anything about the

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<v Speaker 1>hard disc configuration on your machine, and therefore it can't boot.

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<v Speaker 1>More modern computers are not quite so dependent on the

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<v Speaker 1>Sea Moss RAM. They store their settings in non volatile

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<v Speaker 1>RAM that works without any power at all. If the

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<v Speaker 1>battery goes dead, the clock fails, but the computer can

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<v Speaker 1>still boot using the information in this non volatile RAM area. Then,

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<v Speaker 1>once the computer can see the network, you can query

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<v Speaker 1>a time server from the network and set the clock

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