Random Bugs #1: How do computers measure time without power?

Random Bugs #1

Why is the sky blue? Where does the wind come from? How do birds fly? And why do you cry while cutting onions?

Sounds familiar? Then you are going to love this series. It doesn’t? Well, try asking such questions now – after all, it does make your life more interesting and fun to live!

I have always been an extremely curious person, and quite a thinker too. Sometimes it’s no fun – I tend to struggle with certain activities I don’t particularly enjoy (like driving a vehicle), because I think too much. Not saying that’s bad, but I think about random things. You can imagine wondering about the color of the clouds is not the right thing to do when you’re sitting behind the wheel – and I agree, that’s why I don’t drive 🙂 .

If we skip these inappropriate situations though – oh, thinking and wondering is priceless! Not only entertaining and oftentimes educational, you can put it to good use! Like skipping stupid conversations you don’t really want to be a part of (doing this without the other participants noticing takes some skill though) or seemingly hastening your public transportation travels – Indeed, why does the time flow faster when you’re having fun?

Introducing Random Bugs

There are myriads of question of this kind. Throughout my life, I’ve found myself asking some of them over and over again, and never really bothering to get an answer. Over-and-over-again. They just kept bugging me. And I’ve met with people doing the same thing. At certain point, I figured this can’t go on forever and I finally have to satisfy my curiosity. That’s why I’ve decided to bring up this series of posts – each one attempting to answer one of these little buggers in a fairly simple way. Perhaps one day it will make someone happier for a brief moment. Oh, and if you happen to have some interesting questions on your mind, feel free to post them in comments! I always like new inspiration. But enough babbling, today’s question is…

#1: How do computers measure time without power?

You know what I mean. When you’re working on your computer and your computer skills are higher than the sea level, you have your time and date set right and you use your computer as a clock and calendar as well.

Then you turn your computer off for a night, turn it on again in the morning, and it still knows exactly what day and time it is. Understandable – you left the power cable plugged in and so, even if you turned your machine down, it might have been in sort of “Stand By” mode and the clock could keep ticking.


How do they keep the track of time?

Another experiment. This time, you plug the cable off for the night. After a good night’s sleep, you plug the cable in, turn your computer on and find out that the clock is still precise. You silly thing! You forgot you have a notebook and you left the battery plugged in. One more time – and now, no mistakes. You plug the cable off, do the same with the battery and just to make sure, you leave your notebook for a week (like that would happen, eh?).

But, even after the week and with no power what-so-ever, the clock is still all right. Seriously, what magic is this? How does the computer do that?

Answering the question

Well, I hate to disappoint you (and I was quite disappointed when I found out), but the answer is so simple it makes the question sound dumb. There is no magic, no internet-free synchronization with satellites, no radioactive isotopes and there are no little time measuring fellas hidden inside your computer.

What is hidden there however, is a little thing called Real-time clock. This tiny component uses crystal oscillators or some other fancy schmancy piece of technology to keep track of current time – but that’s not really the point here. What is the point is – how does it do its business when you cut the power off?

It turns out you simply don’t. Even if you plug out all the cables and external batteries, there is still some power flowing into it. The trick is, there is a backup battery built into your machine’s motherboard. A tiny little lithium coin cell battery called CMOS Battery that can keep the clock alive for several years without external power. Slick, eh?

And that answers today’s little mystery – now it’s never going to bug you again. Satisfied? I am. Got anything else on your mind? Let me know! And see you next time 🙂 .

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