RSX-11

For the automobile, see Acura RSX.

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-11S -- a memory-resident version of RSX-11M used in embedded real-time applications.
• RSX-11M-Plus -- a much extended version of RSX-11M, originally designed to support the multi-processor PDP-11/74 (http://groups.google.com.au/groups?selm=7656%40shlump.nac.dec.com&rnum=2), 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-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.
• P/OS -- A version of RSX-11M-Plus that was targeted to DEC's PRO-300, PRO-350, and PRO-380 line of PDP-11-compatible personal computers.
• DOS/RV, OCPB-CM -- Two names for the clandestine clone of RSX-11M that was produced behind the Iron curtain. This system appeared to be an exact duplicate of RSX-11M save that the prompt was changed in the binary files. (According to other sources, RSX-11M source code might have been stolen by KGB. If read as Cyrillic, the name OCPB is an abbreviation for 'Operatsionnaya Sistema Realnogo Vremeni' -- the Russian for 'Real Time Operating System'. Not surprisingly, the six-character string 'OCPBCM' fits nicely in the same 16-bit RADIX-50 word as 'RSX11M'.)

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" (http://www3.sympatico.ca/n.rieck/docs/Windows-NT_is_VMS_re-implemented.html) page.

Contents

1 Quotation 2 RSX-11 trivia 3 See also 4 External links

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 (http://www3.sympatico.ca/n.rieck/docs/Windows-NT_is_VMS_re-implemented.html) to Inside Windows NT

RSX-11 trivia

• In order to support large programs within the PDP-11's relatively small virtual address space of 64KB, a sophisticated semi-automatic overlay system was used; for any given program, this overlay scheme was produced by RSX's taskbuilder program (called TKB). If the overlay scheme was especially complex, taskbuilding could take a rather long time. Outside the office of the engineer in charge of ongoing maintenance of the taskbuilder was a whiteboard labeled "Taskbuilder wishlist". For several years, the top item on the wishlist was "same day service".

• Before DCL, the usual RSX prompt was ">" or "MCR>", standing for the "Monitor Console Routine".

• When run on certain PDP-11 processors, each version of RSX displayed a characteristic light pattern on the front of the processor any time the system was idle (and the processor was executing the PDP-11 WAIT instruction). The RSX-11M light pattern was two sets of lights that swept outwards to the left and right from the center of the light display (or inwards if the IND indirect command file processor program was currently running). The IAS light pattern was a single bar of lights that swept leftwards.

See also

• QIO
• AST
• Event flag
• RSTS/E
• RT-11

External links

• Dan Brevik posted a history of precursors to RSX-11 (http://groups.google.com/groups?selm=g11Va.162679%24ye4.109589%40sccrnsc01&output=gplain) in alt.sys.pdp11 (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&safe=off&group=alt.sys.pdp11).

• Dan's RSX-11 prehistory (http://www.demillar.com/RSX/) 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 (http://www.spies.com/~aek/) posted some further notes on RSX-11 (http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&safe=off&selm=bij4na%24r8v%241%40spies.com) in alt.sys.pdp11 (http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&safe=off&group=alt.sys.pdp11).de:RSX-11