During the past several years a computer-aided design system (the Logic Machine) has been under development in our laboratory. Briefly, the Logic Machine consists of a microprogrammable control processor, one or more functional units, one or more bidirectional buses, and a microprogram all arranged to perform a specific digital algorithm. Our major goal has been to be able to construct any digital device with this system. We have been able to build a graphics display terminal (1), a floating point processor (2), string/array auxiliary processor (3), and a minicomputer (4). It has amazed us to see how simple and fruitful it has been to construct these devices. In this paper we describe the use of the Logic Machine design system to build still another digital device, a high-level language minicomputer.

Except for a few notable examples, all computers have been designed as "adder-central" architectures. "Adder-central," as used here, refers to an organization which places the Arithmetic Logic Unit (ALU) at that junction of the system through which all data must flow — thus creating a bottleneck. In the early days, when adders were expensive, cost considerations precluded more than one ALU. Nowadays powerful ALU's are available at very low cost and a designer, even of minicomputers, can consider placing more than one ALU in a system.

A digital electronic hardware design and construction system is described. Basic to the system is a microprogrammed control processor which is used unmodified in all devices constructed using this technique. This processor has no data manipulation capabilities; all arithmetic, logic, and I/O capabilities are supplied by logically complete hardware modules called functional units. The processor supplies control signals on 256 unique instruction lines. Each of these instruction lines can be wired as a control signal to one or more functional units. A control signal may cause data transfer between functional units, test the status of a functional unit, or cause a functional unit to perform a specific internal function. A single data bus connects each of the functional units and the control processor such that the flow and manipulation of data are controlled by a microprogram. A logic machine refers to the ensemble of control processor, single data bus, several functional units, and a microprogram all arranged so that a specific digital system is constructed.