While reading a book, I came across a paragraph given below:

In order to synchronize all of a computer’s operations, a system clock—a small quartz crystal located on the motherboard—is used. The system clock sends out a signal on a regular basis to all other computer components.

And another paragraph:

Many personal computers today have system clocks that run at 200 MHz, and all devices (such as CPUs) that are synchronized with these system clocks run at either the system clock speed or at a multiple of or a fraction of the system clock speed.

Can anyone kindly tell:

  • What is the function of the system clock? And what is meant by “synchronize” in the first paragraph?
  • Is there any difference between “system clock” and “CPU clock”? If yes, then what is the function of the CPU clock?
up vote 13 down vote accepted

The system clock is needed to synchronize all components on the motherboard, which means they all do their work only if the clock is high; never when it's low. And because the clock speed is set above the longest time any signal needs to propagate through any circuit on the board, this system is preventing signals from arriving before other signals are ready and thus keeps everything safe and synchronized. The CPU clock has the same purpose, but is only used on the chip itself. Because the CPU needs to perform more operations per time than the motherboard, the CPU clock is much higher. And because we don't want to have another oscillator (e.g. because they also would need to be synchronized), the CPU just takes the system clock and multiplies it by a number, which is either fixed or unlocked (black edition models).

The system clock switches from zero and one at a million times per second rate. The frequency in the system clock is the number of cycles that happens each second, normally at 66 million per second. The CPU is basically the brains of the computer which means without it, there is no computer. The CPU is the most important element. The CPU has clock cycles to carry out each instruction.


  • 1
    How exactly this answers the question? – Evil Sep 29 '16 at 20:49

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