DOS-15 System Manual

This document serves as a comprehensive system manual for Digital Equipment Corporation's DOS-15 operating system, targeting system programmers, software specialists, and maintenance personnel. It outlines the system's architecture, internal operation, and maintenance.

The manual covers the following key areas:

• DOS Operation: Details the initial system loading and configuration using DOSSAV and DOSGEN, and the interaction between the Resident and Nonresident Monitors with the System Loader.
• Resident Monitor: Describes the core, always-resident part of DOS-15, including the CAL Handler, error processors (.MED and Expanded Error Processor), timing features, and control characters. It acts as the primary interface between the user/devices and running programs.
• Nonresident Monitor: Explains how this component decodes user commands, manipulates system registers and information blocks (like .SCOM, .DAT, .UFDT, SYSBLK, COMBLK, SGNBLK), and initiates system program loading via the System Loader.
• System Loader and Linking Loader: These components are responsible for loading the Resident Monitor, core-image system programs, device handlers, and allocating necessary buffers. The Linking Loader specifically handles user programs.
• System Information Blocks and Tables: Provides in-depth descriptions of various core-resident (.SCOM) and disk-resident (SYSBLK, COMBLK, SGNBLK, Overlay Table, Device Table, IOC Table, .DAT, .UFDT, Skip Chain, RCOM Table, Mass Storage Busy Table) data structures vital for DOS-15 operation.
• File Structures: Details the organization of files on different storage media, including DECtape (non-directoried and directoried), Magnetic Tape (with file directories and labels), and Disk (Master File Directory, User File Directory, buffers, Storage Allocation Tables, and Bad Allocation Tables).
• Writing New I/O Device Handlers: Offers guidance for programmers to develop custom I/O device handlers, including setting up skip chains, API software-level channels, and managing interrupts.
• BOSS-15: Describes an integrated batch operating system that allows sequential job execution, supports a subset of DOS programs, includes a line editor, and uses "Procedure Files" for command expansion.

The manual provides flowcharts and detailed descriptions of routines and tables, illustrating the intricate workings and interdependencies of DOS-15 components for effective system management and expansion.