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Beginning of the Minicomputer

In November 1960, the first PDP-1 computer was delivered. This machine and the 49 other PDP-1s that followed established Digital Equipment Corporation in the computer business. Four and a half years later, in April 1965, the first PDP-8 was delivered. This machine, and the 40,000 PDP-8s that followed, established the concept of minicomputers, leading the way to a multibillion dollar industry. In the chapters of Part II, the development of DEC's 12-bit and 18-bit computers are explored in detail, with special attention paid to the factors influencing their development, the technology used in their implementation, and the reception of each machine in the marketplace. Sections of these chapters were co-authored by the designers or key project team members of the machine where possible. This permits a glimpse into the thoughts of the designers as they recollect and critique the designs in the light of subsequent developments.

Chapter 6 begins with a discussion of the PDP-l, showing the influence of various M.I.T. machines and exploring the design goals of the PDP-l, many of which are only speculations at this late date. The discussion of the PDP-l is followed by brief discussions of the PDP-4, PDP-7, and PDP-9. The PDP-15, the most significant of the 18-bit machines in terms of longevity, number in use, and product range, is also discussed. The architectural changes that made the PDP-15 substantially different from the PDP-4, 7, and 9 are not included in the PDP-15 discussion, but an interesting retrospective view of the design goals and decisions is included. Thus, this section provides a good model of how design should be carried out and reviewed - hopefully, on an a priori basis.

The final section of Chapter 6 on 18-bit machines compares them in terms of cost, performance, and physical metrics. This section can be read independently of the machine design descriptions. Here, it is important for designers to realize that there is a continuity to design and that subsequent designs have to be better along one or more of the evaluation dimensions. Ignoring or not understanding the dimensions can lead to failure in the marketplace.

Chapter 7 describes the PDP-5 and the PDP-8 Family of 12-bit machines. The original PDP-8 is described, along with the various implementations of the same instruction set that occurred over the following fifteen years. Included is a brief discussion of the latest implementation, a computer on a single 40-pin chip. The chapter concludes with a discussion of the technology, price, and performance of the 12-bit computers, including a number of charts.

Chapter 8 is a top-down, hierarchical description of the implementation of the PDP-8 computers; it is based on material from Computer Structures by Bell and

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