What is a Clock Wire in a computer and what is it for?


What is a Clock Wire in a computer and what is it for?

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It’s important for a computer that everything happens in synchronisation, so one of the components is a clock generator. It’s job is to create a signal with a very regular pulse that all of the other components can use to be in sync with one another. All of the components’ actions are timed by receiving that clock signal.

The clock wire pulses every so often (every so often once every slightly less than a billionth of a second) to tell a computer when to update. The problem is that at a very, very low level of computer architecture, you are using wires that are energized to represent true (or 1) and not energized to represent false (or 0), and performing logic on them, and performing that logic takes different amounts of time. This can cause problems if the logic one one wire takes less time than the logic on another wire.

Let’s say I have a weird self-destruct program on my PC that will blow up my computer if A and not A are ever true at the same time. In theory this should never go off, because that’s impossible, right? The problem is that when I change the value of A, it changes the value of A practically immediately, but not A takes very very very slightly more time to update, because it has to go through what is called an inverter, which changes the value of whatever is input it to the opposite. So if I have A at false, not A is true. But when I change A to true after it was false, for a very brief instant the wire that has A on it is true *and* the inverter is still outputting true from the A that was false still propagating through. For a fraction of a fraction of a moment, the self destruct program thinks A is true and not A is true at the exact same time, and boom, my computer explodes.

How do we solve this (other than not having a self-destruct option on our computer for some nonsensical reason)? We add a clock pulse to our computer. We say, hey, don’t update everything right away; only check things when the clock pulses and says it’s been long enough for those signals to work their way through the logic stuff. Thus, even though your self destruct program will still see both A and not A as true for a brief moment, the next clock pulse won’t happen until after the system has gotten everything correct, and my computer is safe. The clock wire is the wire that carries this pulse and tells components, okay, it’s been long enough, update.

It pulses at the clock speed and basically tells all the components to do a step. Whatever operation the computer is trying to do, it first takes the necessary bits from memory and loads them into the correct circuit, and then runs through the circuit, and then takes them from the circuits outputs and put them back into memory.

These operations are happening across thousands of circuits in the computer, and to make sure the signals don’t run over each other or crash into each other, they are all coordinated to happen at the same time.

Others have answered what the clock signal is for but you perplexingly asked about the clock Wire. Are you talking about the wire that connects from the front panel on your computer case to a jack on the motherboard? If so that is connected to a switch and will toggle the computer speed between two different settings. Honestly it is a bit of a legacy thing these days as I’m not sure any modern systems use it any more. But it was very commonly used in machines in the 286-486 days. The reason you would toggle the speed is a lot of software back then, particularly games, were written expecting a specific system speed. If you ran it on a newer faster computer it could run too fast and in the case of games make them difficult to play and with other software it may straight up crash. So if you had to run older programs you may use that clock button to toggle to a slower speed.