PDP-6 Time Sharing System

This document describes the PDP-6 Time Sharing System, an integrated hardware and software solution designed to enhance the efficiency and reduce the cost of data processing. It aims to overcome limitations of conventional systems, such as the inability for users to interact with their programs during execution and inefficient input-output operations that often require separate peripheral processors.

The system provides several key advantages:

1. Time-shared access: Users can interact with the PDP-6 facilities via local or remote teleprinters (user-consoles), enabling on-line debugging and faster turnaround times for program development and execution.
2. Efficient I/O equipment use: Leveraging a priority interrupt system and resident programs, peripheral processing can occur concurrently with program execution, eliminating the need for a separate peripheral processor and reducing system delays caused by I/O waits.
3. Modular software: The system's software is designed for modularity, allowing for easy program modifications, inclusion of new functions, and equipment expansions.
4. Stacked job processing: It supports conventional batch processing, integrating it seamlessly with on-line operations through a single control language.

Key hardware features that support time-sharing include a modular and flexible design, Executive Mode hardware for memory protection against illegal access, large core memory capacity (up to 262,144 36-bit words) with fast auxiliary file storage options (magnetic drums, Micro Tape), and uniform data representation using ASCII code. A minimum system configuration is outlined, including components like the Arithmetic Processor, Memory Module, Micro Tape System, and Teleprinter.

The software framework is built around the PDP-6 Operating System, which includes:

• Supervisory Control Program: Coordinates the entire system, managing user commands (via the Command Control Program), scheduling programs for execution (Program Scheduler), allocating resources (Facilities Allocator), decoding commands, and controlling I/O operations (I/O Control).
• System Programs: Implement specific functions requested by users, such as the Editor Program for text manipulation, Peripheral Conversion Program for efficient data handling, Inter-Console Message Program for user communication, Linking Loader for program assembly, Translator Dispatcher, FORTRAN II Compiler, and MACRO-6 Assembly Program.
• System Subroutines: Provide essential functions like I/O Format Control and various Arithmetic Subroutines, along with a Debugging Program (DDT) for assembly language program debugging.

A typical user interaction involves logging in, storing programs (from cards, paper tape, or direct input), translating them using compilers like FORTRAN II or MACRO-6, debugging with DDT, and finally requesting output or submitting the program for stacked job processing.