Cache is a fast buffer memory between the processor and the main memory and has been extensively used in the larger computer systems. The principle of operation and the various designs of the cache in the uniprocessor system are well documented. The memory system of multiprocessors has also received much attention recently; however, they are limited to the systems without a cache. Little if any information exists in the literature addressing the principle and design considerations of the cache system in the tightly coupled multiprocessor environment. This paper describes such a cache design. System requirements in the multiprocessor environment as well as the cost-performance trade-offs of the cache system design are given in detail. The possibility of sharing the cache system hardware with other multiprocessing facilities (such as dynamic address translation, storage protection, locks, serialization, and the system clocks) is also discussed.