A processor architecture containing multiple closely coupled processors in a form of symmetric multiprocessing system is provided. The special coupling mechanism allows it to speculatively execute multiple threads in parallel very efficiently. Generally, the operating system is responsible for scheduling various threads of execution among the available processors in a multiprocessor system. One problem with parallel multithreading is that the overhead involved in scheduling the threads for execution by the operating system is such that shorter segments of code cannot efficiently take advantage of parallel multithreading. Consequently, potential performance gains from parallel multithreading are not attainable. Additional circuitry is included in a form of symmetrical multiprocessing system which enables the scheduling and speculative execution of multiple threads on multiple processors without the involvement and inherent overhead of the operating system. Advantageously, parallel multithreaded execution is more efficient and performance may be improved.