RSX-11
Encyclopedia
RSX-11 is a family of real-time operating system
s mainly for PDP-11
computers created by Digital Equipment Corporation
(DEC), common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972. It was designed for and much used in process control, but was also popular for program development.
Garth Wolfendale was the project leader for RSX-11D from 1972–1976 and led the redesign and commercial release of the operating system as well as adding support for the 22-bit PDP-11/70 system. Dr Wolfendale, originally from the U.K. set up the team that designed and prototyped IAS in the U.K. providing time-shared user access to operating system resources. Andy Wilson then led the full development and release of the IAS system, based in Digital's U.K. development facility.
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 conceptual descendant of RSX-11M but is more directly descended from an object based operating system Cutler developed for a RISC processor (PRISM
) which was never released. This lineage is made clear in Cutler's foreword to "Inside Windows NT" by Helen Custer.
operating system. RSX-11 provided features to ensure less than a maximum necessary response time to peripheral device input (i.e. real-time processing), its intended use. These included the ability to lock a process (called a task under RSX) into memory as part of system boot up and to assign a process a higher priority so that it would execute before any processes with a lower priority.
Real-time operating system
A real-time operating system is an operating system intended to serve real-time application requests.A key characteristic of a RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter...
s mainly for PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
computers created by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
(DEC), common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972. It was designed for and much used in process control, but was also popular for program development.
Garth Wolfendale was the project leader for RSX-11D from 1972–1976 and led the redesign and commercial release of the operating system as well as adding support for the 22-bit PDP-11/70 system. Dr Wolfendale, originally from the U.K. set up the team that designed and prototyped IAS in the U.K. providing time-shared user access to operating system resources. Andy Wilson then led the full development and release of the IAS system, based in Digital's U.K. development facility.
Dave Cutler
Dave Cutler
David Neil Cutler, Sr. is an American software engineer, designer and developer of several operating systems including RSX-11M, VMS and VAXELN at Digital Equipment Corporation and Windows at Microsoft.- Personal history :...
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
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
system is a conceptual descendant of RSX-11M but is more directly descended from an object based operating system Cutler developed for a RISC processor (PRISM
DEC PRISM
PRISM was a 32-bit RISC instruction set architecture developed by Digital Equipment Corporation . It was the final outcome of a number of DEC research projects from the 1982–1985 time-frame, and was at the point of delivering silicon in 1988 when the management canceled the project...
) which was never released. This lineage is made clear in Cutler's foreword to "Inside Windows NT" by Helen Custer.
Versions
RSX-11 existed in many versions:- RSX-11A, C — small paper tape real time executives.
- RSX-11B — small real time executive based on RSX-11C with support for disk I/O. To start up the system, first DOS-11 was booted, and then RSX-11B was started. RSX-11B programs used DOS-11 macros to perform disk I/O.
- RSX-11D — a multiuser disk-based system. Evolved into IAS.
- IAS — a timesharing-oriented variant of RSX-11D released at about the same time as the PDP-11/70. The first version of RSX to include DCL (Digital Command LanguageDIGITAL Command LanguageDCL, the DIGITAL Command Language, is the standard command languageadopted by most of the operating systems that were sold by the former Digital Equipment Corporation...
), which was originally known as PDS (Program Development System). - 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-11S applications were developed under RSX-11M.
- 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.
- RSX-20F — PDP-11/40 front end processor operating system for the DEC KL10 processor. Derived from RSX-11M.
- Micro/RSX — a pre-generated full version of RSX-11M-Plus with hardware autoconfiguration, 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 the DEC ProfessionalDEC Professional (computer)The Professional 325 and Professional 350 were PDP-11 compatible microcomputers introduced in 1982 by Digital Equipment Corporation as high-end competitors to the IBM PC...
line of PDP-11PDP-11The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
-based personal computers.
Clones in the USSR
- DOS/RV, — Two names for the clandestine clone of RSX-11M that was produced in the Socialist bloc. This system appeared to be an exact duplicate of RSX-11M save that the prompt was changed in the binary files. The full RSX-11M source code was always delivered with the distribution of the operating system (and used in the system generation process), so it was easy to make a copy. If read as Cyrillic, the name ОСРВ is an abbreviation for 'Операционная Система Реального Времени' — the Russian for 'Real-time Operating System'. Not surprisingly, the six-character string 'OCPBCM' fits nicely in the same 16-bit RADIX-50RADIX-50RADIX-50, commonly called Rad-50 or RAD50, is a character encoding created by Digital Equipment Corporation for use on their DECsystem, PDP, and VAX computers...
word as 'RSX11M'. Two last symbols 'СМ' is an abbreviation for 'Система Малых [электронно-вычислительных машин]' — the Russian for 'System of the Small [electronic computation machines]' (SM). 'СМ ЭВМ' is the name of DEC compatible computers developed in USSR (although not all of the СМ ЭВМ was compatible with PDP-11).
- There are differences between RSX and ОСРВ because of differences between SM and PDP hardware and Soviet engineers fixed bugs in RSX. (ОСРВМ is the next model of ОСРВ-СМ for the SM-1425.) RSX11M, however, was used more often than rewritten ОСРВ, because of better work by the RSX-11 re-coders, stability of patched RSX, and a faster update cycle for SM-RSX drivers and patches made possible by the SM users community.
Quotes
- "RSX was a separate path at DEC and the progenitor more than anything of VMS that went to NT via Dave Cutler." — Gordon BellGordon BellC. Gordon Bell is an American computer engineer and manager. An early employee of Digital Equipment Corporation 1960–1966, Bell designed several of their PDP machines and later became Vice President of Engineering 1972-1983, overseeing the development of the VAX...
, Vice President, Research and Development, Digital Equipment Corporation.
- "My purpose was to come up with a good acronym and then find some appropriate words to justify it. ... Oh, by the way, the acronym stood for Real-Time System Executive. Years later that was changed to Resource Sharing Executive, which I think is even better." — Dennis J. Brevik who designed the forerunner RSX-15, about which Brevik said: "At first I called the new system DEX-15. It was an acronym for Digital's Executive - for the PDP-15".
- "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." — Dave Cutler
Operation
RSX-11 was often used for general-purpose timeshare computing, even though this was the target use for the RSTS/ERSTS/E
RSTS is a multi-user time-sharing operating system, developed by Digital Equipment Corporation , for the PDP-11 series of 16-bit minicomputers. The first version of RSTS was implemented in 1970 by DEC software engineers that developed the TSS-8 time-sharing operating system for the PDP-8...
operating system. RSX-11 provided features to ensure less than a maximum necessary response time to peripheral device input (i.e. real-time processing), its intended use. These included the ability to lock a process (called a task under RSX) into memory as part of system boot up and to assign a process a higher priority so that it would execute before any processes with a lower priority.
RSX-11 trivia
- In order to support large programs within the PDP-11's relatively small virtual addressVirtual addressIn computer technology, a virtual address is an address identifying a virtual, i.e. non-physical, entity.-Description:The term virtual address is most commonly used for an address pointing to virtual memory or, in networking, when referring to a virtual network address...
space of 64 KBKilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
, 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 whiteboardWhiteboardA whiteboard is a name for any glossy, usually white surface for nonpermanent markings. Whiteboards are analogous to chalkboards, allowing rapid marking and erasing of markings on their surface...
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". All commands could be shortened to their first three characters when entered and correspondingly all commands were unique in their first three characters. Only the login command of "HELLO" could be executed by a user not yet logged in. Not so much to be friendly, "HELLO" was used as the login command because only the first three characters, "HEL", were relevant and this allowed a non-logged in user to execute a "HELP" command which was passed to the "HEL" command processing program and handled.
- When run on certain PDP-11 processors, each DEC operating system displayed a characteristic light pattern on the front of the processor in the "Data" lights when the system was idle. In RSX, this light pattern was created by an idle task that ran at the system's lowest scheduling priority. The light pattern was produced when the processor displayed the contents CPU register R0 when the "WAIT" instruction was executed. 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). By contrast, the IAS light pattern was a single bar of lights that swept leftwards. Correspondingly, a jumbled light pattern (reflecting memory fetches) was a visible indication that the computer was under load as this meant that the system idle task was not being run. Other PDP-11 operating systems such as RSTS/E had their own distinctive patterns in the console lights.
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 1950s for the RW-300 process control computer (by TRWTRWTRW Inc. was an American corporation involved in a variety of businesses, mainly aerospace, automotive, and credit reporting. It was a pioneer in multiple fields including electronic components, integrated circuits, computers, software and systems engineering. TRW built many spacecraft,...
). (Via archive.org, version fetched April 4, 2005) - Al Kossow posted some further notes on RSX-11 in alt.sys.pdp11.