The CPU clock synchronizes the operation of all parts of the PC and provides the basic timing signal for the CPU. Using a quartz crystal, the CPU clock breathes life into the microprocessor by feeding it a constant flow of pulses.
For example, a 200 MHz CPU receives 200 million pulses per second from the clock. A 2 GHz CPU gets two billion pulses per second. Similarly, in any communications device a clock may be used to synchronize the data pulses between sender and receiver.
A “real-time clock,” also called the “system clock,” keeps track of the time of day and makes this data available to the software. A “time-sharing clock” interrupts the CPU at regular intervals and allows the operating system to divide its time between active users and/or applications.