1 00:00:00,520 --> 00:00:03,840 Speaker 1: Welcome to Brainstuff from house Stuff Works dot com where 2 00:00:03,840 --> 00:00:15,200 Speaker 1: smart happens. Hi am Marcia Brain with today's question, why 3 00:00:15,280 --> 00:00:19,520 Speaker 1: does your computer need a battery? Most computers have a 4 00:00:19,600 --> 00:00:22,880 Speaker 1: small battery about the size of a nickel. The battery 5 00:00:22,920 --> 00:00:25,599 Speaker 1: is usually in some sort of holder that sits on 6 00:00:25,640 --> 00:00:29,160 Speaker 1: the motherboard so it's easy to replace. Computers are not 7 00:00:29,240 --> 00:00:31,680 Speaker 1: the only things that have a small battery like this. 8 00:00:32,040 --> 00:00:35,800 Speaker 1: Camcorders and digital cameras often have them as well. Just 9 00:00:35,920 --> 00:00:38,960 Speaker 1: about any gadget that keeps track of time. We'll have 10 00:00:39,040 --> 00:00:42,319 Speaker 1: a little battery in your computer as well as these 11 00:00:42,360 --> 00:00:45,760 Speaker 1: other gadgets. The battery powers a chip called the real 12 00:00:45,840 --> 00:00:49,600 Speaker 1: time clock chip. The real time clock is essentially a 13 00:00:49,680 --> 00:00:52,920 Speaker 1: courtz watch that runs all the time whether or not 14 00:00:53,000 --> 00:00:57,280 Speaker 1: the computer has power. The battery powers this clock. When 15 00:00:57,280 --> 00:00:59,800 Speaker 1: the computer boots up, part of the process is to 16 00:01:00,040 --> 00:01:02,880 Speaker 1: query the real time clock chip to get the correct 17 00:01:02,920 --> 00:01:06,200 Speaker 1: time and date. A little quartz clock like this might 18 00:01:06,319 --> 00:01:09,360 Speaker 1: run for five to seven years off that small battery. 19 00:01:09,720 --> 00:01:12,959 Speaker 1: Then it's time to replace the battery. In many cases, 20 00:01:13,080 --> 00:01:16,800 Speaker 1: once the battery fails, your computer will no longer boot up. 21 00:01:17,240 --> 00:01:19,679 Speaker 1: You would expect the computer to boot fine, but have 22 00:01:19,760 --> 00:01:22,840 Speaker 1: an incorrect time and date. The reason your computer will 23 00:01:22,880 --> 00:01:26,440 Speaker 1: not boot is because the real time clock chip also 24 00:01:26,480 --> 00:01:30,319 Speaker 1: contains sixty four or more bytes of random access memory 25 00:01:30,840 --> 00:01:34,600 Speaker 1: known as the se Moss RAM. The clock uses ten 26 00:01:34,680 --> 00:01:38,440 Speaker 1: bytes of this space, leaving fifty four bytes for other purposes. 27 00:01:38,840 --> 00:01:42,160 Speaker 1: The bios stores all sorts of information in the sims 28 00:01:42,280 --> 00:01:45,880 Speaker 1: RAM area, like the number of drives, the hard disc 29 00:01:46,000 --> 00:01:49,280 Speaker 1: drive type, and stuff like that. If the sms RAM 30 00:01:49,360 --> 00:01:52,440 Speaker 1: loses power, the computer may not know anything about the 31 00:01:52,480 --> 00:01:56,320 Speaker 1: hard disc configuration on your machine, and therefore it can't boot. 32 00:01:56,640 --> 00:01:59,720 Speaker 1: More modern computers are not quite so dependent on the 33 00:01:59,760 --> 00:02:03,440 Speaker 1: Sea Moss RAM. They store their settings in non volatile 34 00:02:03,520 --> 00:02:06,400 Speaker 1: RAM that works without any power at all. If the 35 00:02:06,400 --> 00:02:09,280 Speaker 1: battery goes dead, the clock fails, but the computer can 36 00:02:09,360 --> 00:02:14,040 Speaker 1: still boot using the information in this non volatile RAM area. Then, 37 00:02:14,160 --> 00:02:16,840 Speaker 1: once the computer can see the network, you can query 38 00:02:16,840 --> 00:02:19,720 Speaker 1: a time server from the network and set the clock 39 00:02:19,800 --> 00:02:24,200 Speaker 1: that way. Be sure to check out our new video podcast, 40 00:02:24,400 --> 00:02:27,240 Speaker 1: Stuff from the Future. Join How Staff Work Staff as 41 00:02:27,320 --> 00:02:31,040 Speaker 1: we explore the most promising and perplexing possibilities of tomorrow. 42 00:02:32,480 --> 00:02:34,480 Speaker 1: The house stuf works. I find app has a rye. 43 00:02:34,639 --> 00:02:36,519 Speaker 1: Download it today on iTunes.