PDP-X Model I Extended Op Simulator Initial Specifications

This document is a technical memorandum (PDP-X Technical Memorandum #34, dated November 17, 1967) detailing the specifications for the "PDP-X Model I Extended Op Simulator."

The document describes a software simulator designed to allow PDP-X Model I users to execute "extended op" (EOP) instructions normally reserved for Model II hardware. By residing in core memory, the simulator intercepts trapped EOP instructions, performs the necessary calculations (including arithmetic, logic, stack operations, and shifts), and updates registers and condition codes before returning control to the user program. This process is intended to be invisible to the user, providing Model I systems with expanded functionality without requiring additional hardware.

The report includes detailed lists of the simulated EOP instructions, descriptions of the simulator's internal routines (SAV, EOP, and RET), memory stack management, error recovery procedures, and comprehensive flow charts for the various simulation subroutines.