A central processing unit (CPU) is an important part of almost every computer. The CPU sends signals to control the other parts of the computer, almost like how a brain controls a body.
The CPU is an electronic machine that works on a list of things to do, called instructions. It reads the list of instructions and does (executes) each one in order. A list of instructions that a CPU can run is a computer program.
The speed that a CPU works at is measured in hertz (Hz). Modern processors often run so fast that gigahertz (GHz) is used instead. One gigahertz is one billion cycles per second.
Most CPUs used in desktop (home) computers are made by either Intel or Advanced Micro Devices (usually shortened to AMD). Some other companies that make CPUs are ARM, IBM, and Sun Microsystems. Their CPUs are usually used for more specialized things, like in mobile phones, cars, game consoles, or in the military.

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