IAS Executive Facilities Reference Manual

This manual serves as a comprehensive reference for the IAS (Interactive Application System) Executive, detailing its facilities, design, and operational mechanisms within the PDP-11 hardware environment.

It is structured into six chapters and two appendices, covering:

• Executive Design Considerations: An overview of PDP-11 hardware memory management, including the Processor Status Word and virtual/physical addressing, as well as how IAS utilizes memory mapping through Active Page Registers and facilitates Executive-task communication via EMT, MFPI, and MTPI instructions.
• Executive Services: Descriptions of fundamental services such as system directives, significant events, and event flags for task synchronization. It elaborates on system trapping mechanisms (Synchronous System Traps for execution-related faults and Asynchronous System Traps for external events like I/O completion) and various intertask communication techniques (event flags, shareable global areas, dynamic regions, SEND/RECEIVE data blocks, and shared data files).
• System Data Structures: A detailed look into the crucial components of IAS system data structures, including fixed-length tables, linked lists, and node accounting. It outlines the Active Task List, System Task Directory, Physical Unit Directory, Task Partition Directory, Global Common Directory, and various queues and lists used for I/O requests, clock scheduling, asynchronous traps, intertask communication, spawned tasks, and memory management. It also describes the contents of task headers.
• Memory Allocation and Scheduling: Explanations of IAS's three partition types (user-controlled, system-controlled, and timesharing), the task scheduling mechanism, system checkpointing for real-time tasks, swapping for scheduler-controlled tasks, the use of fixed tasks, and memory protection.
• Shareable Global Areas (SGAs): A focus on SGAs, their types (resident libraries, common areas, installed regions), their installation and removal, and their role in memory efficiency and intertask data sharing.
• Input/Output Facilities: Coverage of logical units, device assignments, device handler tasks, Queue I/O (QIO) system directives, spooling (automatic output and input), and the I/O rundown process initiated when a task exits without completing I/O operations.

The appendices further provide formats for system lists and tables and a listing of QIOMAC.LST, supporting a deep understanding of the IAS Executive for programmers.