A clock may refer to any of the following:
1. In general, the clock refers to a microchip that regulates the timing and speed of all computer functions. In the chip is a crystal that vibrates at a specific frequency when electricity is applied. The shortest time interval any computer can observer is one clock cycle, or one vibration of the clock chip. The speed of a computer processor is measured in clock speed, for example, 1 MHz is one million cycles, or vibrations, a second. 2 GHz is two billion cycles, or vibrations, a second.
2. Another name for the internal clock or RTC (real-time clock).
3. A system clock or system timer is a continuous pulse that helps the computer clock keep the correct time. It keeps count of the number of seconds elapsed since the epoch, and uses that data to calculate the current date and time.
4. Clock is the name of a transition.