The CPU clock dictates how fast the processor can process the data, and a microprocessor having a clock speed of 3 MHz means that it can process data internally 3 million times a second at every clock cycle.
The crystal quartz oscillator is the most appropriate frequency determining device in virtually all microprocessors, microcontrollers, PICs and CPUs; It is used to generate their clock waveforms. To generate a microprocessor clock, generally, all you need is crystal and two ceramic capacitors of values ranging 15 to 33 pF as demonstrated below:
Most microprocessors, microcontrollers and PICs have two oscillator pins labelled OSC1 and OSC2 to connect to an external quartz crystal, RC network or even a ceramic resonator. In this application, the crystal oscillator produces a train of continuous square wave pulses whose frequency is controlled by the crystal which in turn executes the instruction that control the device.
Also read: The Basic Principle of Operation of an Oscillator
