Central Processing Unit
A central processing unit is the hardware in a computer that carries out (executes) the instructions of a computer program or command input by the user. They are used to process and execute arithmetic and logical operations. On larger machines they need one or more printed circuit boards. On PC's and small workstations the CPU is housed in a silicon chip called a microprocessor. The clock rate affects the speed at which it can perform, so several gigahertz is very fast, at about a billion 'ticks' a second per gigahertz. Speed is measured in hertz (Hz), with most computers being in MHz (megahertz) and the most powerful computers being several gigahertz per second.