Monitor Calls

The DECsystem-20 Monitor Calls User's Guide introduces assembly language programmers to the functions and monitor calls available on the DECsystem-20. It covers key topics including:

• Basic I/O: Using monitor calls for terminal input/output and number conversions.
• File Management: How to associate files with Job File Numbers (JFNs), open, transfer data, and close files.
• Software Interrupt System: Managing asynchronous signals and conditions that break the normal flow of control.
• Process Structure: Understanding jobs, processes, and how to create, control, and communicate between them.
• Inter-Process Communication Facility (IPCF): Using packets and PIDs for inter-process messaging.
• Enqueue/Dequeue (ENQ/DEQ) Facility: Managing resource sharing and avoiding "deadly embraces" in concurrent systems.

The manual is organized by function, progressing from simple tasks to advanced system interactions, and serves as an introductory text to complement the more comprehensive DECsystem-20 Monitor Calls Reference Manual.