A front-end processor (FEP) is generally a computer or processing unit that produces and manipulates data before another computer or processor receives it. (A processor is generally a shortened name for a microprocessor or a central processing unit (CPU).) FEPs are so called because they go between the communications lines (that sometimes directly connect into the processor) and the processor itself. The front-end processor is sometimes synonymous with a communications controller (an intermediary device used in transferring communications to and from the host ("main") computer to which it is connected), though the latter is usually not as flexible in its functions as that of an FEP.

Front-end processors were invented to reduce routine teleprocessing functions on processors within mainframe computers. Later FEPs were designed to be inexpensive to install and maintain in order to reduce using the higher priced CPUs. Front-end processors were engineered to provide...