IBM 3081 Processor Unit: Design Considerations and Design Process

Significantly new challenges were presented for the design of the 3081 Processor Unit since it was the first IBM large system implemented in LSI technology. Solutions had to be found for a new set of problems in order to achieve the required product objectives while maintaining an acceptable development cost and schedule. In this paper, the design aspects and the characteristics of the 3081 Processor Unit are described and the tradeoffs that were made due to the implementation of LSI are presented. A design strategy was chosen that included tradeoffs covering the areas of machine organization, performance level, implementation costs, testing and servicing aids, and development schedules. An innovative verification effort was introduced into the design process, capitalizing on a hardware flowcharting discipline and rigorous design rules. On the basis of this development experience, some thoughts concerning VLSI implementations are explored.