Douglas B. MacGregor

The Motorola MC68020

This new 32-bit microprocessor provides high performance, instruction set extensibility, and compatibility with existing M68000 family software.

A Performance Analysis of MC68020-based Systems

T he determination of processor performance during the early stages of design is essential to the proper analysis of design trade-offs as well as to the evaluation of product viability. This problem is common to both the developer of the processor and the developers of systems based on the processor. In each case, an understanding of the processors behavior is essential to proper design. Here, we describe a method for estimating the performance of the MC68020, a 32-bit microprocessor, and computer systems based on the 68020. We undertook two separate studies in developing this methodology. First, we devised a general model of computation for the 68000 by tracing typical programs executing on a 68000-based workstation. From these traces, we developed a profile of instruction frequency that served as a model for processor execution. Second, we made traces of bus activity in a 68000-based Hewlett-Packard 9000, Series 200, Model 236 computer. We used these traces to develop a model of bus behavior-a model that includes locality, types of accesses, and DMA activity. (This model was later used in the design of the new HP 9000, Series 300 computer family.) By combining these models, we can predict the performance characteristics of the 68020 microprocessor and any system based on the 68020. In this article, we will examine the models to understand the factors affecting performance of the processor and a system based on the processor. We will then correlate the predicted performance characteristics to the 68020 chip and system, respectively, to determine the validity of our method. When developing processor-specific computation models that will be used to evaluate performance, determine resource utilization, and describe the nature of processing, one should avoid comparing the results to those produced by a different architecture. However, the methods we used to develop the models of computation and bus behavior are applicable to, and valuable for, the evaluation of any architecture.

Virtual Memory and the MC68010

The designers of this microprocessor used the continuation method to provide an elegant general solution to the problem of virtual memory support.