In computer engineering, an execution unit (also called a functional unit) is a part of a CPU that performs the operations and calculations called for by the computer program. It may have its own internal control sequence unit (not to be confused with the CPUs main control unit), some registers, and other internal units such as a sub-ALU or FPU, or some smaller, more specific components.
It is common for modern CPUs to have multiple parallel execution units, referred to as scalar or superscalar design. The simplest arrangement is to use one, the bus manager, to manage the memory interface, and the others to perform calculations. Additionally, modern CPUs' execution units are usually pipelined.