COMPUTER SYSTEM PERFORMANCE

Evolution of Computer System Performance

Abstract

Computer system improvement has been, and always will be, significantly influenced by the underlying trends and capabilities of hardware and software technologies. The transition from electromechanical relays to vacuum tubes to transistors to integrated circuits has driven fundamentally different trade-offs in the architecture of computer systems. Additional advances in software, which includes the transition of the predominant approach to programming from machine language to assembly language to high-level procedural language to object-oriented language, have also resulted in new capabilities and design points. The impact of these technologies on computer system architectures past, present, and future will be explored and projected.

Evolution of Computer System Performance

Introduction

The key hardware technologies that affect computer architectures are those that determine the density and speed of digital switches and the density and access time of digital storage. Figure 1 shows the trend in increasing capacity and performance for digital switching technologies. The important trend to notice is that capacity improves at a more rapid rate than transistor speed. The trends in capacity and access time for two important digital storage technologies: dynamic random access memories and magnetic disk storage. Here again, the important trend reflected is that capacity is improving at a faster rate than time taken to access the data stored. These basic trends have been true throughout the history of computer systems and are projected to continue through the foreseeable future in the absence of fundamentally new technological approaches. (Auslander, 1981)

Discussion

Despite these underlying trends, the performance of computer systems has increased at a rate which exceeds the rate of improvement in transistor speed and digital storage access speeds. To achieve this, computer systems have been required to take approaches that improve performance by exploiting both technological density and speed. Since these basic trends are projected to continue, future system designs can be expected to leverage both density and speed to achieve additional system performance.

In the earliest computer systems, both density and speed were quite modest; and software technologies were very immature. These facts drove computer architectures, which used very simple instructions and register sets combined with machine level programming, to provide the maximum in efficient exploitation of the limited number of switches and storage capacity. As hardware became denser and faster, the number of registers and the complexity of the instruction sets were increased. Advancing software technology allowed programming to move to the assembly language level and, eventually, ...