Central Processing Unit
The CPU is the 'brain` of the computer.
It is where all the sarching, sorting, calculating and decision making takes place.
The CPU contains a tiny quartz clock. Each time this clock 'ticks`, one instruction can be dealt with by the CPU. So the more times this clock ticks per second, the more instruction the CPU can carry out and the faster things get done.
The speed of the CPU is measured in either Megahertz (MHz) or more commonly now in Gigahertz (GHz).
A1 MHz CPU can carry out one million instructions per second. A1 GHz CPU can carry out 1 billion instructions per second.
Atypical CPU installed in a computer today would run at around 3 GHz.