Extension of PDP-11 Instruction Set

This document explores several proposed methods for extending the basic PDP-11 instruction set to accommodate the requirements of a more elaborate machine, referred to as the PDP-K. The author, Ad van de Goor, evaluates four main approaches: implementing 'pure stack' instructions, using a flag-based instruction indicator, employing processor modes, and utilizing reserved multiply/divide opcode space.

Each solution is tested against five representative coding problems involving floating-point arithmetic and multi-dimensional array operations. Based on metrics including the number of instructions, total words, and memory references, the document concludes that a 'multiply/divide' subsolution is the most promising, providing significant performance improvements for array handling despite the trade-off of a more complex instruction set.