IAS Executive Facilities Reference Manual

The IAS Executive Facilities Reference Manual (Version 3.4, May 1990) provides technical documentation for the IAS Executive operating system on PDP-11 hardware. The manual details the design philosophy of the executive, focusing on how it manages memory (including Active Page Registers, virtual addressing, and shared use of processor registers) and coordinates tasks.

Key areas covered include:

• Memory Management and Mapping: Describes how the system maps memory segments, including the Executive, System Communication Area (SCOM), External Page, user tasks, and shareable global areas (SGAs).
• Executive Services: Details system directives, event flag synchronization, and system traps, including both Synchronous System Traps (SSTs) and Asynchronous System Traps (ASTs) with their associated service routines.
• System Data Structures: Provides an in-depth look at internal system data structures, such as fixed-length tables, linked lists, the Active Task List (ATL), System Task Directory (STD), and node accounting mechanisms.
• Scheduling and Allocation: Covers partition types (user-controlled, system-controlled, and timesharing), real-time task scheduling, memory allocation strategies, and the mechanisms for checkpointing and swapping tasks to disk.
• Input/Output Facilities: Explains the logical unit (LUN) and device assignment system, device handler tasks, Queue I/O (QIO) directives, and the spooling of input/output operations.
• Reference Material: Includes appendices documenting system lists, tables, and the QIOMAC macro definitions used for standard I/O directives.