Digital Modules, The Basis for Computers

The circuits and design concepts described in Chapter 4 were the basis for the subsequent development of DEC modules. In Chapter 5, the discussion of this development is broadened to include not only circuits and design concepts but also packaging and the effects of progress in semiconductor technology. DEC modules are important because the progress in semiconductor technology that has formed the major element of the technology push driving the computer industry is evident in the history of DEC modules on a scale convenient for close examination and understanding.

The first modules produced by DEC were called Digital Laboratory Modules and were intended to sit on an engineer's workbench or be mounted in a scientist's equipment rack. To facilitate the rapid construction of logic systems using these modules, interconnection was accomplished with simple cords equipped with banana plugs. As shown in Figure 1, the modules were mounted in aluminum cases 1-3/4 X 4-1/2 X 7 inches in size. All of the logic signals were brought out to the front of the case, where they appeared on miniature banana jacks mounted in a schematic diagram of the logic function performed by the module. The modules were offered in three speed ranges with compatible signal levels. The three speed ranges were 5 MHz (1957), 500 kHz (1959), and 10 MHz (1960).

The Digital Laboratory Module product line was supplemented by the Digital Systems Modules. These modules, samples of which are

Figure 1. Digital Laboratory Modules.