Overview

Most operating systems texts present a chapter on the broad history of operating systems. We deviate from this practice by looking at this history as it took shape in a single company, Digital Equipment Corporation. This approach is justified because the flow of computer history is similar either way. For instance, the development of time-sharing operating systems was taking place on four machines simultaneously in the middle 1960s: Digital's PDP-1, IBM's 7090, Burrough's B5000, and SDC's AN/FSQ-32V. Concentrating on a specific company, rather than simply marking the stages of that development, we can, perhaps, lend some insight into the reasoning behind certain decisions made and directions taken by the company's management and engineers. Incidentally, because this chapter comes after all the technical material has been presented, we can use the correct terminology in describing the evolution of the various operating systems concepts.

It should be obvious that the history of operating systems is also the history of hardware systems; for example, paging and interrupts are software concepts that must be supported by hardware. As stated, the hardware is designed to support the requirements of the operating system and the customer, as well as the technology. Although early computers did not emphasize this philosophy, it gained acceptance over time, reaching its epitome in the VAX and Reduced Instruction Set Computer (RISC) designs. These two machine classes were jointly designed by hardware engineers, operating system designers, compiler designers, and so forth, to optimize total system performance.

From the outset, Digital wanted...