A Real-Time Multiple Task Executive Program with a Built-in Console Utility Package for PDP-8/S and PDP-8 Computers

This document describes a real-time executive program developed at Oak Ridge National Laboratory for PDP-8 and PDP-8/S computers. The program allows for the scheduling of up to eight process control tasks with assigned priorities, coordinating input-output equipment, and managing time-based execution.

Key features and components include:

• Real-Time Scheduling: The system utilizes a hardware clock interrupt and internal counters (cycles and minutes) to manage task timing.
• Memory Usage: The executive and utility package occupy a small portion of the computer's 4K memory, leaving the majority available for system tasks.
• Task Management: Tasks are organized by priority (0–7) and tracked through status, location, period, and offset tables.
• Console Utility Package: An integrated toolset allows operators to communicate with the computer, perform memory operations, manage paper tapes, and debug programs via mnemonic commands.
• Interrupt Handling: The system manages interrupts for power status, the real-time clock, keyboard input, printer output, and parity (for the PDP-8/S).
• Operational Requirements: The program uses fixed-point arithmetic for efficiency, as the developers found floating-point arithmetic to be too slow for these systems. Detailed instructions are provided for loading, configuring, and maintaining tasks within the executive framework.