Interactive Application System
{{Short description|Old DEC operating system}}
{{use mdy dates|date=September 2020}}
{{use American English|date=September 2020}}
{{Infobox OS
| name = Interactive Application System (IAS)
| logo =
| screenshot =
| caption =
| developer = Digital Equipment Corporation
| programmed_in =
| family = RSX-11
| working_state = Discontinued
| source_model =
| released = {{Start date and age|1975}}
| latest_release_version = 3.4
| latest_release_date = {{Start date and age|1990|05}}
| marketing_target =
| language = English
| updatemodel =
| package_manager =
| supported_platforms = PDP-11
| kernel_type =
| influenced_by = RSX-11D
| ui = PDS or MCR Command-line interface
| license = Proprietary
| website =
}}
Interactive Application System (IAS) was a DEC operating system for the PDP-11.{{cite web |website=BitSavers |date=May 1990
|url=http://bitsavers.org/pdf/dec/pdp11/ias/v3.4/IAS_3.4A_SPD_May1990.pdf
|title=IAS_3.4A_SPD_May1990 PDF}} It was a fork from RSX-11D."D" for Disk, since 11A & 11C were paper-tape based{{cite web
|url=http://s3data.computerhistory.org/pdp-1/dec.digital_1957_to_the_present_(1978).1957-1978.102630349.pdf
|title=DIGITAL EQUIPMENT CORPORATION - Nineteen Fifty-Seven To The Present (PDF). Digital Equipment Corporation. 1975.}}
The last major release, Version 3.0, began distribution late 1979;{{cite web
|url=http://www.bitsavers.org/pdf/dec/pdp11/catalogs/AV-3468J-TC_SysSwCataOct79.pdf
|title=PDP-11 System Software Component Catalogue |date=October 1979}} the final version, 3.4, came out May 1990.
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" (with RSX-11M Plus being a followup). IAS was designed to a mix of "concurrent timesharing, real-time and batch."{{cite news |newspaper=Computerworld
|title=PDP-11/70 new multifunction operating system: IAS (Interactive Application System)
|date=April 23, 1975 |page=25}}{{cite news |newspaper=Computerworld
|title=Newly announced PDP-11/70 operating system
|date=February 26, 1975 |page=35}} A looking back described it as "bare basics .. handled interrupts .. scheduled processes, and provided interprocess communications" without being "all things to all people."{{cite web
|url=https://forums.theregister.com/forum/all/2007/06/20/usenix_07_opening_keynote
|title=Interactive Application System (IAS) Anyone?
|quote=file systems, databases, .. etc were applications called by other applications
|date=June 21, 2007
|access-date=September 17, 2020
|archive-date=April 21, 2021
|archive-url=https://web.archive.org/web/20210421233326/https://forums.theregister.com/forum/all/2007/06/20/usenix_07_opening_keynote/
|url-status=dead
}} Another description, rather than focusing on taking away overhead, wrote "IAS (Interactive Application System) was created by adding two things to 11D."{{cite web
|title=DECUS US chapters
|url=http://bitsavers.org/pdf/dec/decus/DECUS_SIG_Newsletters/DECUS_US_Chapters_SIG_Newsletters_V02_N07_Mar1987.pdf
|date=March 1987}}
RSX-11's use of a version number as part of a file's identifier: MYFILE.DAT;3{{cite web
|title=PDP-11 Software Handbook |year=1978
|url=http://www.bitsavers.org/pdf/dec/pdp11/handbooks/PDP11_Software_Handbook_1978.pdf}} was retained by IAS.
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.{{rp|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).{{rp|p.1}}{{rp|p.28}}"Inter-task transmission .. region access"
IAS provided two different Command Language Interpreter (CLI) interfaces - the RSX-11 MCR, and the Program Development System (PDS). PDS was an early implementation of the Digital Command Language.{{cite book|title=IAS MCR User's Guide |url=https://bitsavers.org/pdf/dec/pdp11/ias/v3.4/AA-H006C-TC_IAS_MCR_Users_Guide_199005.pdf |date=May 1990 |publisher=Digital Equipment Corporation}}
DEC's Sort/Merge utility program was distributed as part of IAS.{{rp|p.10}}
Performance
The system can be operated in one of three modes: Real-Time, Multi-User, and Timesharing.{{cite book
|chapter=Performance evaluation of IAS on the PDP-11/70
|author1=R. Turner |author2=H. Levy |title=Proceedings of the 1976 ACM SIGMETRICS conference on Computer performance modeling measurement and evaluation - SIGMETRICS '76
|year=1976|pages=71–74
|doi=10.1145/800200.806183
|s2cid=36177762
}}
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.{{rp|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."{{rp|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."{{rp|p.28}}
The heuristic timesharing scheduler tracks "history of performance and degree of interaction."{{rp|p.29}}
Some failure recovery is built into both the DEC hardware and IAS software.{{cite report |website=apps.DTIC.mil
|title=Tactical Operations Analysis System (TOAS) Baseline Configuration
|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a086750.pdf
|author=G. Slaton |year=1980
|archive-url=https://web.archive.org/web/20190429085243/https://apps.dtic.mil/dtic/tr/fulltext/u2/a086750.pdf
|url-status=live
|archive-date=April 29, 2019}}