A central processing unit ( CPU )—also called a central processor
or main processor —is the most important processor in a given computer.
Its electronic circuitry executes instructions of a computer program, such as
arithmetic, logic, controlling, and input/output (I/O) operations. This role
contrasts with that of external components, such as main memory and I/O
circuitry, and specialized coprocessors such as graphics processing units
(GPUs).
The form, design, and implementation of CPUs have changed over time, but their
fundamental operation remains almost unchanged.