Processing in memory: the Terasys massively parallel PIM array

SRC researchers have designed and fabricated a processor-in-memory (PIM) chip, a standard 4-bit memory augmented with a single-bit ALU controlling each column of memory. In principle, PIM chips can replace the memory of any processor, including a supercomputer. To validate the notion of integrating SIMD computing into conventional processors on a more modest scale, we have built a half dozen Terasys workstations, which are Sun Microsystems Sparcstation-2 workstations in which 8 megabytes of address space consist of PIM memory holding 32K single-bit ALUs. We have designed and implemented a high-level parallel language, called data parallel bit C (dbC), for Terasys and demonstrated that dbC applications using the PIM memory as a SIMD array run at the speed of multiple Cray-YMP processors. Thus, we can deliver supercomputer performance for a small fraction of supercomputer cost. Since the successful creation of the Terasys research prototype, we have begun work on processing in memory in a supercomputer setting. In a collaborative research project, we are working with Cray Computer to incorporate a new Cray-designed implementation of the PIM chips into two octants of Cray-3 memory.>