The CPU, short for central processing unit, performs the primary arithmetic, logic and control functions of a computer. The CPU is made up of two primary components: the arithmetic logic unit, which handles the arithmetic and logic functions, and the control unit, which handles the control functions.
CPUs have two primary measures of speed: integer rate and clock rate. Computer commands are essentially just on and off commands, represented by one and zero, respectively. The integer rate describes how many on and off commands a CPU can handle at one time. For example, an 8-bit CPU can handle eight on and off commands at a time, whereas a 64-bit CPU can handle 64 on and off commands at a time.
Clock rate simply refers to how many times the integer rate can repeat in a second. The higher the clock rate, the faster the CPU.