PDP-11 Subprogram Calling Conventions

This document, an interoffice memorandum from Hank Spencer dated November 10, 1970, establishes a standard calling convention for subroutines on the PDP-11 computer. It outlines the requirements considered, such as execution speed, code length, reentrancy support, and variable-length argument lists. The memorandum details the approved calling sequence using JSR and BR instructions, providing examples of both simple and reentrant calls, and notes that this standard was intended for implementation in the Fortran compiler.