Several recent and proposed computer systems have employed parallel and pipelined architectures to increase instruction execution rate, or throughput. These vary from the giant ILLIAC IV1 with its large number of processing elements constrained to perform nearly identical computations in unison (single instruction stream-multiple data stream9) to the Carnegie-Mellon C. mmp system2 employing a number of independent minicomputers with shared memory (multiple instruction stream-multiple data stream). On the other hand, pipelining has been used in numerous' large computers, such as the Control Data 6600, 7600, and STAR, the IBM System 360/91 and 360/195, and the Texas Instruments ASC, to improve throughput. These systems generally employ single instruction stream-single data stream processing, although some machines in this category also have “vector” instructions that operate on multiple data streams.