Publisher Summary
This chapter focuses on Digital Equipment Corporation (DEC) PDP-11. Minicomputer can be used in a number of ways, namely, communications controller, instrument controller, large-system preprocessor, real-time data acquisition systems, and desk calculator. In some applications, current minicomputers have limitations. These limitations show up when the scope of their initial task is increased. The DEC PDP-11 Model 20 is the first computer of a computer family, which is designed to span a range of functions and performance. The Model 20 can nominally be classified as a third generation, 16-bit word, one central processor with eight 16-bit general registers, using two's complement arithmetic and addressing up to 216 8-bit bytes of primary memory. The computer's components are connected via a single switch, called the Unibus. The types of messages in the PDP-11 are along the lines of the hierarchical structure, common to present-day computers. The single bus makes conventional and other structures possible. The PDP-11 Unibus has 56 bidirectional signals conventionally used for program-controlled data transfers, direct memory data transfers, and control-to-processor interrupt.