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Clock Signals, Cycle Time and Frequency
As I mentioned in the previous page of this section, the dimension of change in the operation of signals is time. Signals change as time progresses, and this is what enables the flow of data, in fact, everything that happens within a PC. With so many circuits within a computer, it is necessary for some sort of synchronization to occur. Otherwise, the PC would be a like a symphony without a conductor.
The "conductor" of the PC is the system clock. A clock is just a signal that alternates between zero and one, back and forth, at a specific pace. In many ways, it is just like a metronome, going back and forth over and over. The clock sets the "pace" for everything that happens within a particular electronic circuit.
There are a few important terms and attributes related to clock signals, which you will occasionally hear mentioned:
Where do these clock signals come from in the first place? That's a very good question. In fact, they are generated the same way that a digital watch (or any electronic timepiece) keeps time. A special circuit called an oscillator supplies a small amount of electricity to a crystal. Crystals are special components made out of components such as quartz, which vibrate at a particular frequency when energized. By controlling the characteristics of the crystal and the rest of the circuit, the specific speed of the clock can be determined fairly precisely. Some oscillator circuits also provide additional components to allow the same crystal to generate a variety of different clock speeds, perhaps even under software control.
Note: In some contexts, a clock
signal may be called a strobe or other similar name.
Next: Derived System Clocks