The PDP-10 Family
This final part of Computer Engineering contains only a single chapter, "The Evolution of the DECsystem 10." It is a fitting conclusion because it summarizes many of the aspects of computer engineering discussed in the rest of this book. The introduction and historical setting with which the chapter begins are condensations of the historical information included in Parts I and II of this book; the goals, constraints, and design decisions elaborated on in the remainder of the chapter are specific examples of the concepts discussed throughout the book. The paragraph headings, such as "logic," "fabrication," "packaging," and ''price/performance,'' have counterparts in earlier chapters.
The authors of this chapter, which first appeared as a paper in the January 1978 issue of Communications of the A CM, have been key figures in the evolution that they describe. Thus, when they talk about design decisions and tradeoffs, they are talking from first-hand experience.
The 36-bit Family has been important to DEC for a number of reasons. The designers of these machines have realized that software development is very costly, and have put a great deal of emphasis on making their systems easy to program, even if additional hardware expense is involved. Furthermore, their hardware has been very conservatively designed, with rigid design rules to assure that the vast number of circuits required to implement each function operate correctly under all conditions. Although the chapter conclusion suggests that the PDP-l0 engineers have transferred hardware technology to minicomputer engineering, the technology transfer has been principally in the area of automated design aids, as it has only been with the ECL logic of the KL10 that PDP-l0 designs have used logic families or module technology not previously used in the minicomputer segment of DEC. The paragraphs on "logic" and "packaging" within the main body of the chapter elaborate on this.
The role of the PDP-6 in PDP-l0 history is described in detail in the chapter, but it has interesting aspects in addition to those mentioned. Because the PDP-6 was the first computer to offer elegant, powerful capabilities at a low price, a great many of the PDP-6s built found their way into university and scientific environments, giving DEC a strong foothold in that market and providing both educated customer input for future models and a source of bright young future employees to assist in the hardware and software development for those future models. The impact of the PDP-6 was particularly noteworthy because fewer PDP-6s were built than any other DEC machine: only 23. The sales were sufficiently disappointing to management, in fact, that a decision was made (but fortunately