A horizontally structured microprogrammable processor (AMP) designed as a tool for microcontrol, language, and processor design research, is described. The machine employs a minimally encoded microcontrol word, a very general multiple bus structure, highspeed local storage, several arithmetic/logic units, and completely asynchronous memory referencing. These features combine to yield substantial low-evel parallelism and a highly versatile microinstruction. In addition, hardware modification is easily accomplished, further supporting the experimental nature of the processor.