DOS-15 System Manual

This document serves as a comprehensive system manual for the DOS-15 operating system, primarily intended for systems programmers, DEC Software Specialists, and internal maintenance programmers. It details the system's architecture, internal operations, and maintenance procedures.

The manual outlines the three main components of the DOS-15 Monitor:

1. Resident Monitor: The always-present core component, responsible for basic I/O, error handling, system bootstrapping, and timing features. It interfaces between the operator/devices and the running program.
2. Nonresident Monitor: Loaded by the System Loader, it decodes user commands, manipulates system parameters stored in various blocks and tables (.SCOM, .DAT, .UFDT, SYSBLK, COMBLK, SGNBLK), and orchestrates system modifications.
3. System Loader and Linking Loader: These components manage the loading of the Resident Monitor, system programs, device handlers, and user programs, as well as buffer allocation.

The document provides in-depth information on file structures for various storage devices, including DECtape (non-directoried and directoried), Magnetic Tape, and Disk, detailing their organization, directories, and data recording methods. It also covers crucial system information blocks and tables, their contents, and how they are used by different parts of the system.

A significant portion is dedicated to guiding users on how to write new I/O device handlers for DOS-15, including setting up interrupt channels, handling interrupts, and managing communication with the PDP-11 in UC15 systems.

Finally, the manual introduces BOSS-15, an optional batch processing system that extends DOS-15 capabilities for running sequential jobs, managing accounting, and providing a line editor. Flowcharts and tables are extensively used throughout the document to illustrate processes and data structures.