Chapter 34 The engineering design of the Stretch computer 439
a Double Card, which has 4 times the capacity of a single card and which has wiring on both sides of the board. Furthermore, components are double-stacked; and again, the rail is used to if effect circuit variations due to different applications. Eighteen double card types are used in the system. Approximately 4,000 double cards are used, housing 60% of the transistors. The rest of the transistors are on approximately 18,000 single cards.
The cards, both single and double, are assembled in gates, and two gates are assembled into a frame. Figure 15 shows the gate back-panel wiring, using wire-wraps; and Figs. 16 and 17 the frame construction, both in a closed and open version.
To achieve high performance, special emphasis must be placed on keeping noise to a low level. This required the use of a plane
Fig. 16. The frame (closed).
Fig. 17. The frame (extended).
which overlies the whole back panel, against which the intercircuit wiring is laid. In addition, the power-supply distribution system must be of such a low impedance that extraneous noise cannot induce circuit malfunction. For this reason, a bus system, consisting of laminated copper sheets, is used to distribute the power to each row of card sockets. The wiring rules are such that single-conductor wire is used up to a maximum of 24", twisted pair to a maximum of 36", unterminated coax to a maximum of 60", and terminated coax to a maximum of 100 feet. The whole back-panel construction and the application of single wire, twisted pair, or coax are calculated by a computer program to minimize the noise on each circuit node.
The two gates o a frame are a sliding pair with the power supply mounted on the sliding portion. All connecting wires between frames are coax and arrayed in layers which are formed into a drape.
References
BlaaG59; BrooF57a, 59; BuchW58; DunwS56; RobeJ58; BlosR60; BuchW57, 62; BrooF60; CockJ59; CoddE59, 62.