microprocessors are the most complex and challenging chip designs ever implemented. To stay on the leading edge, Digital's microprocessor designers strive for global optimizations across the design space, develop innovative highspeed custom circuit design techniques, and use state-of-the-art manufacturing technology for fabrication. With microprocessor performance increasing at a rate of 50 % per year, quick time-to-market is crucial. Logic and circuit bugs that would prevent first-pass silicon from booting the operating system must be eliminated before tape out if unacceptable schedules delays are to be avoided. Quick time-to-market is achieved by: fostering good design practice through the use of a consistent methodology and detailed design reviews; accounting for manufacturing variations and long-term reliability concerns from the start of the design; and subjecting the chip models to rigorous logical and electrical verification prior to prototype fabrication. This paper presents a practical view of Digital's design process. I.

Recent advances in multiprogramming have been concentrated on multiprocessor systems. But overlap in operations is also permissible in uniprocessor systems in which the processor instruction execution and input–output operations are handled by separate units. By maximizing the processor and input–output overlap, a program can be executed faster while the system utilization is highly improved.