The i o port architecture for computer modules

In an earlier paper [Bell, et al., 1973] a new set of digital modules* called Computer Modules, or simply CM's, is described. In that paper it was stated that the correct design of the CM i/o structure is critical to their success$ and moreover, the l/o structure of a CM is what distinguishes it from contemporary minicomputers* This report describes a preliminary design of the l/o structure for computer modules. The functions of the l/o ports are discussed here, and it is observed that they must allow sharing of memory and passing of control among interconnected CM's. CM's use a variation of the segmented address space scheme to implement the functions of the l/o port. A complete ISP description of the l/o port is included, as well as a number of examples of inter-CM communications that illustrate the various ways the l/o ports can be used*