PDP-11 Architectural Enhancement Strategy

This document, authored by Dave Nelson in 1975, proposes an architectural shift for the PDP-11 series. The primary goal is to address limitations in the existing I/O architecture by introducing a 'process-structured' approach. This includes defining I/O functions as processes managed by a 32-bit descriptor, enabling faster context switching, higher I/O performance via block multiplexing, and better management of UNIBUS bandwidth. The proposal also outlines the use of microcode-controlled I/O and describes a high-speed serial bus for low-performance peripherals. Extensive performance simulations comparing the proposed improvements against existing configurations and competing architectures (like IBM 370 and others) are included to justify the strategy.