RSX-11 Guide, Meaning , Facts, Information and Description

RSX-11: A family of Real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation (DEC), common in the late 1970s and early 1980s, designed for and much used in process control, but also popular for program development.

It existed in many versions:

• RSX-11/A, C -- small paper tape real time executives.
• RSX-11/B -- small real time executive based on RSX-11/C with support for disk I/O. To start up the system, first DEC DOS was booted, and then RSX-11/B was started by some command that I do not recall. RSX-11/B programs used DEC DOS macros to perform disk I/O.
• RSX-11/D -- evolved into IAS
• RSX-11M -- a multiuser version that was popular on all PDP-11s.
• RSX-11M-Plus -- a much extended version of RSX-11M, originally designed to support the multi-processor PDP-11/74, a computer that was never released, but also used widely as a standard operating system on the PDP-11/70. The first version of RSX to include DCL (Digital Command Language).
• RSX-11S -- a memory-resident version used in real-time applications.
• RSX-20F --11/40 front end processsor operating system for the DEC KL10 processor. Derived from RSX-11S
• Micro/RSX -- a stripped-down version implemented specifically for the Micro PDP-11, a low-cost multi-user system in a box, featuring ease of installation, no system generation, and a special documentation set.

Dave Cutler was the project leader for RSX-11M, which was an adaptation of the earlier RSX-11D for a smaller memory footprint. Principles first tried in RSX-11M later appeared in DEC's VMS. Microsoft's Windows NT system is a distant descendent of RSX-11M but is more directly descended from an object-oriented operating system Cutler developed for a RISC processor which was never released. This lineage is made clear in Cutler's foreword to Inside Windows NT, quoted on Neil Rieck's "Windows-NT" is "VMS re-implemented" page.

Quotation

• "RSX was a separate path at DEC and the progenitor more than anything of VMS that went to NT via Dave Cutler." -- Gordon Bell, Vice President, Research and Development, Digital Equipment Corporation.

• "My first operating system project was to build a real-time system called RSX-11M that ran on Digital's PDP-11 16-bit series of minicomputers. ... a multitasking operating system that would run in 32 KB of memory with a hierarchical file system, application swapping, real-time scheduling, and a set of development utilities. The operating system and utilities were to run on the entire line of PDP-11 platforms, from the very small systems up through the PDP-11/70 which had memory-mapping hardware and supported up to 4 MB of memory." -- David Cutler, foreword to Inside Windows NT

External links

• Dan Brevik posted a history of precursors to RSX-11 in alt.sys.pdp11.

• Dan's RSX-11 prehistory contain documents which trace RSX-11 back through RSX-15 and the real time executive written by John Neblett in the late 50's for the RW-300 process control computer.

• Al Kossow posted some further notes on RSX-11 in alt.sys.pdp11.

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