Dubois A testbed for experimenting with memory hierarchies in multiprocessors is being supported. A processor node in the testbed contains cache and memory system controllers made from field-programmable gate arrays. To experiment with a memory control mechanism or coherency technique, the investigators program the gate arrays to implement the mechanism. For software support of experimental techniques, the GNU-C compiler is being modified to generate appropriate code, such as non-blocking prefetches, and the Mach microkernel is being ported to provide thread scheduling.