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Table Of Contents
Modern Computer Architecture and Organization - Third Edition
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The clock signal is the heartbeat of a processor. This signal is typically a square wave operating at a fixed frequency. A square wave is a digital signal that alternates between high and low levels, spending equal durations at each level on each cycle. Figure 2.17 shows an example of a square wave over time.

Figure 2.17: Square wave signal
The clock signal in a computer system is usually generated from a crystal oscillator with an output frequency of a few MHz. A crystal oscillator relies on the resonant vibration of a crystal, usually made of quartz, to generate a cyclic electrical signal. The mechanical vibration of the crystal is transformed into an electrical signal by the piezoelectric effect. The piezoelectric effect is the electrical charge that accumulates in certain crystals when placed under mechanical stress. Quartz crystals resonate at precise frequencies, which is why they serve as timing elements in computers, wristwatches, and numerous other digital devices.
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