Distributed Computer Systems - A Review

Abstract

The past five years have seen a dramatic changeabout in traditional hardware/software relationships: hardware costs have plummeted, and the size, environmental requirements and reliability of computing elements have altered drastically. It now becomes feasible to distribute a computing system, such that processors may be placed adjacent to the processes they control. These distributed computing modules operate in an essentially parallel mode, but are required to communicate in order to co-ordinate their activities. Reliable, secure communication systems must be established to ensure correct operation. Such systems are not only functions of the electrical hardware employed, but also of the software support provided. Of vital importance are the protocols selected, which define and detail an agreed procedure for the exchange of information. This paper reviews the fundamental software considerations in the design of computer networks, with specific relevance for process-control applications. It discusses in detail, inter-connection strategies and protocols and briefly examines currently adopted schemes. The implications offully decentralized system control are considered. Of particular concern is the question of the production of reliable, fault-tolerant, secure systems.