Interactive Application System

Interactive Application System (IAS) was a DEC operating system for the PDP-11.[1] It was a fork from RSX-11D.[2][3]

Interactive Application System (IAS)
DeveloperDigital Equipment Corporation
OS familyRSX-11
Working stateDiscontinued
Initial release1975 (1975)
Latest release3.4 / May 1990 (1990-05)
Available inEnglish
PlatformsPDP-11
Influenced byRSX-11D
Default
user interface		Command-line interface
LicenseProprietary

The last major release, Version 3.0, began distribution late 1979;[4] the final version, 3.4, came out May 1990.[1]

Overview

DEC's RSX-11A and C were paper tape based, B had limited disk support, "D" was for disk, and the "M" designation was for "small Memory requirement" /later "Multi-user"[3] (with RSX-11M Plus being a followup). IAS was designed to a mix of "concurrent timesharing, real-time and batch."[5][6] A looking back described it as "bare basics .. handled interrupts .. scheduled processes, and provided interprocess communications" without being "all things to all people."[7] Another description, rather than focusing on taking away overhead, wrote "IAS (Interactive Application System) was created by adding two things to 11D."[8]

RSX-11's use of a version number as part of a file's identifier: MYFILE.DAT;3[9] was retained by IAS. [1]: p.2 

The batch facility's command files used the same syntax as the indirect command files available to interactive users; multiple batch jobs could run concurrently.[1]: p.2  The system could be tuned to either leave unused CPU cycles to batch, or to guarantee a minimum level (without taking from Real Time requirements).[1]: p.1 [10]: p.28 [11]

DEC's Sort/Merge utility program was distributed as part of IAS.[1]: p.10 

Performance

The system can be operated in one of three modes: Real-Time, Multi-User, and Timesharing.[10]

Multi-User shares the system with Real-Time tasks; Timesharing adds effective concurrent use of batch processing alongside "noncritical real-time tasks" and interactive users.[10]: pp.10–13  Timesharing also adds Timesharing Control Primitives (TCP), described as a "mechanism for timesharing tasks to invoke and communicate with other timesharing tasks."[10]: p.13  An evaluation by TRW's Defense and Space Systems Group for Tactical Operations Analysis Support Facility at Langley AFB VA highlighted the "IAS heuristic timesharing scheduler" and "subtasking support at the Kernel Executive level via the SPAWN system directive."[10]: p.28 

The heuristic timesharing scheduler tracks "history of performance and degree of interaction."[10]: p.29 

Some failure recovery is built into both the DEC hardware and IAS software.[12]

References
  1. "IAS_3.4A_SPD_May1990 PDF" (PDF). BitSavers. May 1990.
  2. "D" for Disk, since 11A & 11C were paper-tape based
  3. "DIGITAL EQUIPMENT CORPORATION - Nineteen Fifty-Seven To The Present (PDF). Digital Equipment Corporation. 1975" (PDF).
  4. "PDP-11 System Software Component Catalogue" (PDF). October 1979.
  5. "PDP-11/70 new multifunction operating system: IAS (Interactive Application System)". Computerworld. April 23, 1975. p. 25.
  6. "Newly announced PDP-11/70 operating system". Computerworld. February 26, 1975. p. 35.
  7. "Interactive Application System (IAS) Anyone?". June 21, 2007. file systems, databases, .. etc were applications called by other applications
  8. "DECUS US chapters" (PDF). March 1987.
  9. "PDP-11 Software Handbook" (PDF). 1978.
  10. R. Turner; H. Levy (1976). "Performance evaluation of IAS on the PDP-11/70". Semantic Scholar: 71–74. doi:10.1145/800200.806183. S2CID 36177762.
  11. "Inter-task transmission .. region access"
  12. G. Slaton (1980). Tactical Operations Analysis System (TOAS) Baseline Configuration (PDF). apps.DTIC.mil (Report). Archived (PDF) from the original on April 29, 2019.
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