MAC - A Master Subroutine Control System for PDP-1

This document, M-1091 (dated November 22, 1960), introduces the MAC (Master Subroutine Control System) for the PDP-1 computer. The system was developed to:

• Reduce the memory registers required for closed subroutines.
• Enable subroutines to be called recursively.
• Simplify the overall process of writing subroutines.

MAC operates by interpreting the address part of a cal instruction to identify the target subroutine. The document provides detailed instructions for:

• Subroutine Entry/Exit: How to call subroutines and manage returns using jmp variations and cal for specific requirements.
• Calling-Sequence Parameters: Methods for passing parameters, including 'immediate' and 'remote' parameters.
• Recursion: Techniques for protecting return locations and subroutine storage using jsp spl and jsp spn.

The appendix summarizes the available MAC operations, their functions, and their execution times.