The Evolution of the DECsystem-10
C. GORDON BELL, ALAN KOTOK, THOMAS N. HASTINGS, and RICHARD HILL
The project from which the PDP-6, DECsystem-l0, and DECSYSTEM-20 series of scientific, timeshared computers evolved began in the spring of 1963 and continued with the delivery of a PDP-6 in the summer of 1964. Initially, the PDP-6 was designed to extend DEC's line of 18-bit computers by providing more performance at increased price. Although the PDP-6 was not designed to be a member in a family of compatible computers, the series evolved into five basic designs (PDP-6, KA10, KI10, KL10, and KL20) with over 700 systems installed by January 1978. During the initial design period, we neither understood the notions and need for compatibility nor did we have adequate technology to undertake such a task. Each successive implementation in the series has generally offered increased performance for only slightly increased cost. The KL10 and KL20 systems span a five to one price range.
TOPS-l0, the major user software interface, developed from a 6-Kword monitor for the PDP-6. A second user interface, TOPS-20, introduced in 1976 with upgraded facilities, is based on multiprocess operating systems advances.
This paper is divided into seven sections. Section 2 provides a brief historical setting followed by a discussion of the initial project goals, constraints, and basic design decisions. The instruction set and system organization are given in Sections 4 and 5, respectively. Section 6 discusses the operating system, while Section 7 presents the technological influences on the designs. Sections 4 through 7 begin with a presentation of the goals and constraints, proceed to the basic PDP-6 design, and conclude with the evolution (and current state). We try to answer the often-asked questions, "Why did you do...?", by giving the contextual environment. Figure 1 helps summarize this context in the form of a timeline that depicts the various hardware/software technologies (above line) and when they were applied (below line) to the DECsystem- 10.
The PDP-6 was designed for both a time-shared computational environment and real-time laboratory use with straightforward interfacing capability. At the initiation of the project, three timeshared computers were