On Sunday morning, I brought my girlfriend’s computer to my apartment, and set it up Monday evening. But, the time in the lower right hand corner was correct!!! How did this happen?
I don’t even believe in God!!!
Um… it was set by the manufacturer?
There’s a little battery on the motherboard, and the hardware clock runs off that battery. The battery also keeps alive the memory that stores hardware configuration information.
It’s the CMOS battery.
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CMOS is a type of semiconductor device, right? Why do we refer to the battery as a CMOS battery? The battery obviously isn’t a CMOS device. The meory backed up by the battery may be, but then again, just about every chip in the computer is a CMOS device, isn’t it?
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From the CNET.com Glossary:
Are you asking this, or stating this?
I was saying that if the clock was correct, it was obviously set by someone. If it’s a new computer (which I thought was implied by the OP but now I’m not sure) it must have been set when the PC maker built and configured the computer. The fact is that computer clocks run off the memory, and do not lose the time when disconnected from power.
The term “CMOS battery” was shorthand for “the battery that holds information in the ‘CMOS’ part of the computer.” The term “CMOS” has come to mean that part of the computer where it stores its settings that it uses at boot-up. It needs to be low power because its information has to be held with a battery when there’s no AC power. So they use the lowest power ICs available, which are CMOS technology.
By the way, my two HP 12C calculators have been running for 16 years on the original batteries. CMOS at work.
Oh, and one more thing. CMOS devices can hold their state with extremely low power drain. They use more power by a very large factor when switching states. But the clock has to actually be running when the PC is unplugged. It’s good engineering that they can have a circuit to excite a crystal to oscillate, power a resonant circuit, and run a few logic gates to count the oscillations, and not draw too much out of the battery. It’s actually such low power that the limitation for how long they can run is not in discharging the battery, but in the battery’s shelf life.
OK. Then why the question mark after your answer?
For the same reason as we call something a sandwich toaster even though it isn’t made of sandwiches.