A coprocessor is a special set of circuits in a microprocessor chip that is designed to perform some other specialized function more efficiently than the basic microprocessor circuits could perform the same task.

A coprocessor offloads specialized processing operations, thereby reducing the burden on the basic microprocessor circuitry and allowing it to work at optimum speed.

Using FPGA/ASIC technology a custom coprocessor could be build to accelarate particular processing task such as computer arithmetics, graphics, signal processing, string processing or encryption.

Modern FPGAs could be reconfigured on the fly to accelerate more tasks at different times. Clink on the following figure describes how it works. CCC hardware compiler architecture