A functional unit is one of the many individual, but interconnected, hardware and software components (processing units) within the central processing unit (CPU) that as a unified group carries out the functions of the CPU. Each component is responsible for accomplishing one specific aspect of the CPU's over-all function. The CPU consists of minuscule circuitry that serves as the main information processor in a computer. It is generally a single microprocessor made from a small disk of semiconducting material (usually silicon) with millions of electrical components on its surface. The CPU must also be able to reference memory and input/output (I/0) devices in the execution of instructions. In addition, the CPU should be able to recognize and respond to external control signals, such as "wait" and "interrupt" requests.

CPUs are likely to contain functional units that perform such activities as fetching instructions from memory, interpreting...