Pdp-8/e Instruction Simulators for Other Pdp-8s

This document outlines a set of PAL III subroutines developed by Guy L. Steele, Jr. in 1971 to provide instruction compatibility for PDP-8 models lacking the specific hardware features of the PDP-8/E. The PDP-8/E introduced new non-EAE (Extended Arithmetic Element) instructions, such as BSW (Byte Swap) and various MQ register operations, which rendered programs incompatible with older PDP-8 variants.

These subroutines allow users to simulate these specific PDP-8/E instructions on older systems. They are designed to be efficient, callable from anywhere in memory using a page-zero pointer, and invoked using the same mnemonics as the actual hardware instructions, minimizing the need for program revision. The document includes the source code listings for these simulators, notes on their implementation, and restrictions regarding their usage, such as limitations on memory fields and performance trade-offs compared to native hardware execution.