computer system in the context of a memory hierarchy the term u201c below u201d means logically further away from the processor many techniques have been developed to increase the efficiency of a memory hierarchy memory hierarchy efficiency relative to a benchmark program is usually measured by its average access time during the execution of the benchmark program a store cache is a technique that improves average access time by decreasing the workload of a cache in the next cache layer below that of the store cache it does this by accumulating stores to a cache line in a buffer and then writing the contents of the buffer to the cache line in the next layer of cache in one access eliminating the multiple accesses that would have transpired had each separate store performed a store operation in modern computing systems that have multiple processors there is an effort to increase performance by computing parts of a program in parallel on the same processor if the processor is multithreaded and or on multiple different processors and combine or compare results as needed intermittently during an execution this is often accomplished by synchronizing multiple threads of execution on the same or different processors and or making results produced by one thread of execution visible to other threads of execution synchronization is often accomplished by executing u201c atomic u201d instructions and groups of instructions an atomic instruction appears to execute u201c all at once u201d to other threads of execution and to other processors i e the atomic instruction can never be observed to be partially complete in like manner a group of instructions may be made atomic by making their effect visible all at once to other threads and.