Principal Features of Small Digital Computers

Abstract

By this point in the text, readers should appreciate how small computers, minicomputers, operate upon data in response to orders presented sequentially by the instructions of the instruction set according to the Von Neumann concept of a computer. The importance of word-length in determining the range of possible orders and the maximum size of store which may be addressed directly has been stressed in the light of the teaching-aid MIC. However, many important features of real minicomputers remain to be considered. This chapter discusses particularly relevant aspects of computer architecture. Initially a simple 24-bit machine is taken as the example though later the machine is contrasted against a more sophisticated 16-bit minicomputer representative of current computer practice. Detailed gating arrangements necessary to achieve machine operation are not emphasised since they detract from the attempt to provide an overview of computer architecture. Instead, throughout the chapter, the emphasis is on the effect of word-length on instruction set and store capacity. The role of the computer designer as to the choice of the orders of the instruction set is considered.