TOPS-20 Monitor Internals

This document is a comprehensive technical manual detailing the internal logic and architecture of the TOPS-20 operating system's monitor (version 3). It provides in-depth explanations, often accompanied by flowcharts, for various core system functionalities. Key areas covered include:

• Extended Addressing: Details the virtual address space, including 30-bit addresses, sectioning, compatibility, and programming implications with specific instructions.
• Bias Control: Explains the administrative settings for scheduling algorithms to balance interactive and compute-bound jobs.
• Class Scheduling: Describes resource allocation based on user classes, including defining class percentages and managing "windfall" resources.
• Execute-Only: Outlines the capability to protect files from modification while allowing execution, along with associated restrictions for files and processes.
• Monitor Address Space: Explains the organization and management of the monitor's memory, including psects, symbol table handling, and address space rearrangement.
• Monitor Modules: Provides descriptions of various system modules and their functions.
• Watch: Details a data collection tool for analyzing system and job performance, covering metrics such as load averages, directory cache statistics, per-job information, system utilization, and disk I/O.
• Working Set Swapping: Explains the mechanics of swapping processes in and out of memory, including working set data structures and managing process history.
• System Debugging and Crash Analysis: Offers extensive procedures and tools for debugging and analyzing system crashes, utilizing different versions of DDT (UDDT, MDDT, EDDT, FILDDT), BUGHLT macros, SYSERR functions, push-down lists, and methods for mapping monitor pages and recovering from directory errors.
• Coding Conventions: Provides guidelines for JSYS calls and subroutine interfaces within the TOPS-20 environment.