A digital computer's CPU clock is a pulse generator which synchronizes operations throughout the system (or a portion of the system).

The higher the clock speed of a system, the more operations are performed per second. Performing more operations per second will usually lead to a more instructions being performed per second, but the relationship between the clock speed and instruction execution is rarely 1:1.

On CMOS processors (the majority of processors available today), each clock pulse leads to state change within the processor, and therefore to energy consumption. The higher the clock rate, the more energy is consumed, and the more heat is generated.

A clock cycle is the activity provoked by one clock pulse (and the length of time between pulses).

A system's Real Time Clock keeps track of the current date and time.

Clock can also refer to:

• Other pulse signals, similar to the CPU clock but used for other purposes (“The video clock ran much slower than the CPU clock on that system”)
• The process of sequentially transferring bits, usually under control of a clock signal (“The bits are clocked out at 19200 bits per second starting with the most significant bit”)
• Various other timer and counter circuits which generate pulses (such as interrupts) or count pulses or events