Architecture, design, and performance of Application System/400 (AS/400) multiprocessors

The architecture, design, and performance of multiprocessors in the Application System/400® (AS/400®) family are discussed. The paper describes how this multitasking system, originally designed as a uniprocessor system, was modified to form a multiprocessor system. The unique approach, using relatively atomic instructions, required a minimum of change while providing significant performance gains.