Interactive Application System (IAS) was a
DEC operating system for the
PDP-11
The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were so ...
.
It was a
fork
In cutlery or kitchenware, a fork (from la, furca ' pitchfork') is a utensil, now usually made of metal, whose long handle terminates in a head that branches into several narrow and often slightly curved tines with which one can spear foods ...
from
RSX-11D.
The last major release, Version 3.0, began distribution late 1979; the final version, 3.4, came out May 1990.
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Overview
DEC's RSX-11A and C were paper tape
Five- and eight-hole punched paper tape
Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop
Punched tape or perforated paper tape is a form of data storage ...
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." A ''looking back'' described it as "bare basics .. handled interrupts .. scheduled processes, and provided interprocess communications" without being "all things to all people." Another description, rather than focusing on taking away overhead, wrote "IAS (Interactive Application System) was created by adding two things to 11D."
RSX-11's use of a ''version number'' as part of a file's identifier: ''MYFILE.DAT;3'' 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.][ 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).][
DEC's Sort/Merge utility program was distributed as part of IAS.][
]
Performance
The system can be operated in one of three ''modes'': Real-Time, Multi-User, and Timesharing.[ Timesharing also adds ''Timesharing Control Primitives'' (TCP), described as a "mechanism for timesharing tasks to invoke and communicate with other timesharing tasks."][ 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."][
The ''heuristic timesharing scheduler'' tracks "history of performance and degree of interaction."][
Some failure recovery is built into both the DEC hardware and IAS software.]
References
{{Digital Equipment Corporation
DEC operating systems
PDP-11
1975 software
Discontinued operating systems