228 BEGINNING OF THE MINICOMPUTER
7. A high current path flows via the X and Y selection switches, but in an opposite direction to the read case (see item 2). If a 1 is written, no inhibit current is present and the net current in the selected core is -Iswitching. If a 0 is written, the current is -Iswitching +(Iswitching/2) and the core remains reset.
8. The inhibit and write logic signals are turned off at time tmd specified by timing in the memory module, and the memory cycle is completed.
For a discussion of the behavior of the transistor as it is used in these switching circuit primitives, the reader should consult semiconductor electronics and physics textbooks. It is hoped that the reader has gained a sense of how to think about the hierarchical decomposition of computers into particular levels of analysis (and synthesis) and that the hierarchical approach will be of aid in the reading of Part III.
Top, left to right:
. PDT-1 1 programmable data terminal.
Bottom, left to right:
. Model 20 central processor.
. PDP-1 1 packaging showing cabinet level integration.