| RSX-11 | |
| Developer: | Digital Equipment Corporation |
| Source Model: | Closed source
|
| Supported Platforms: | PDP-11 |
| Influenced: | OpenVMS |
| Influenced By: | RSX-15 |
| Ui: | DCL and MCR Command-line interface |
| Programmed In: | MACRO-11, BLISS |
| Prog Language: | FORTRAN-77 BASIC COBOL |
| Working State: | Discontinued |
| License: | Proprietary |
RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later operating systems such as VMS and Windows NT.
As the original Real-Time System Executive[1] [2] name suggests, RSX was designed (and commonly used) for real time use, with process control a major use.[3] [4] It was also popular for program development[5] and general computing.
RSX-11 began as a port to the PDP-11 architecture of the earlier RSX-15 operating system for the PDP-15 minicomputer,[6] first released in 1971.[7] The main architect for RSX-15 (later renamed XVM/RSX) was Dennis “Dan” Brevik.[8] [9]
Commenting on the RSX acronym, Brevik says:[10]
The porting effort first produced small paper tape based real-time executives (RSX-11A, RSX-11C) which later gained limited support for disks (RSX-11B). RSX-11B then evolved into the fully fledged RSX-11D disk-based operating system, which first appeared on the PDP-11/40 and PDP-11/45 in early 1973.[11] The project leader for RSX-11D up to version 4 was Henry Krejci.
While RSX-11D was being completed, Digital set out to adapt it for a small memory footprint, giving birth to RSX-11M, first released in 1973. From 1971[12] to 1976, the RSX-11M project was spearheaded by noted operating system designer Dave Cutler, then at his first project. Principles first tried in RSX-11M appear also in later designs led by Cutler, DEC's VMS and MICA and Microsoft's Windows NT.[13] [14] [15]
Under the direction of Ron McLean a derivative of RSX-11M, called RSX-20F, was developed to run on the PDP-11/40 front-end processor for the KL10 PDP-10 CPU.[16]
Meanwhile, RSX-11D saw further developments: under the direction of Garth Wolfendale (project leader 1972–1976) the system was redesigned and saw its first commercial release. Support for the 22-bit PDP-11/70 system was added. Wolfendale, originally from the UK, also set up the team that designed and prototyped the Interactive Application System (IAS)[11] operating system in the UK; IAS was a variant of RSX-11D more suitable for time sharing. Later development and release of IAS was led by Andy Wilson, in Digital's UK facilities.
Below are estimated release dates for RSX-11 and IAS. Data is taken from the printing date of the associated documentation. General availability date is expected to come closely after. When manuals have different printing dates, the latest date is used. RSX-11S is a proper subset of RSX-11M, so release dates are always assumed to be the same as the corresponding version of RSX-11M. On the other side, RSX-11M Plus is an enhanced version of RSX-11M, so it is expected to be later than the corresponding version of RSX-11M.
| Date | RSX-11A, C | RSX-11D | IAS | RSX-11M, S | RSX-11M Plus | Micro/RSX | Comment | |
|---|---|---|---|---|---|---|---|---|
| March 1973[17] | RSX-11A 1.0 | |||||||
| May 1973[18] | RSX 11D 1.0 | |||||||
| December 1973[19] | RSX-11C 7A | Final release of RSX-11C | ||||||
| November 1974[20] | RSX-11M 1.0 | |||||||
| June 1975[21] | RSX-11D 6.2 | Final version of RSX-11D | ||||||
| September 1975 | RSX-11M 2.0 RSX-11S 2.0 | RSX-11S 1.0 never existed | ||||||
| December 1975 | IAS 1.0 | |||||||
| April 1977 | RSX-11M 3.0 RSX-11S 3.0 | |||||||
| December 1977 | RSX-11M 3.1 RSX-11S 3.1 | |||||||
| May 1979 | RSX-11M 3.2 RSX-11S 3.2 | RSX-11M Plus 1.0 | ||||||
| bef. October 1979[22] | IAS 3.0 | Final major release of IAS | ||||||
| November 1981 | RSX-11M 4.0RSX-11S 4.0 | RSX-11M Plus 2.0 | ||||||
| April 1983 | RSX-11M 4.1 RSX-11S 4.1 | RSX-11M Plus 2.1 | ||||||
| July 1985 | RSX-11M 4.2 RSX-11S 4.2 | RSX-11M Plus 3.0 | Micro/RSX 3.0 | |||||
| September 1987 | RSX-11M 4.3 RSX-11S 4.3 | RSX-11M Plus 4.0 | Micro/RSX 4.0 | Final Micro/RSX version | ||||
| May 1988 | RSX-11M 4.4 RSX-11S 4.4 | RSX-11M Plus 4.1 | ||||||
| January 1989 | RSX-11M 4.5 RSX-11S 4.5 | RSX-11M Plus 4.2 | ||||||
| January 1990 | RSX-11M 4.6 RSX-11S 4.6 | RSX-11M Plus 4.3 | ||||||
| May 1990[23] | IAS 3.4 | Final IAS Release | ||||||
| February 1993 | RSX-11M 4.7 RSX-11S 4.7 | RSX-11M Plus 4.4 | Last release from Digital Equipment | |||||
| March 1995 | RSX-11M Plus 4.5 | |||||||
| November 1998 | RSX-11M 4.8 RSX-11S 4.8 | Released by Mentec | ||||||
| February 1999 | RSX-11M Plus 4.6 | Micro/RSX 4.6 | Released by Mentec |
RSX-11 is proprietary software. Copyright is asserted in binary files, source code and documentation alike. It was entirely developed internally by Digital. Therefore, no part of it is open source. However a copy of the kernel source is present in every RSX distribution, because it was used during the system generation process. The notable exception to this rule is Micro-RSX, which came with a pre-generated autoconfiguring binary kernel. Full sources was available as a separate product to those who already had a binary license, for reference purposes.
Ownership of RSX-11S, RSX-11M, RSX-11M Plus and Micro/RSX was transferred from Digital to Mentec Inc. in March 1994[24] as part of a broader agreement.[25] Mentec Inc. was the US subsidiary of Mentec Limited, an Irish firm specializing in PDP-11 hardware and software support. In 2006 Mentec Inc. was declared bankrupt while Mentec Ltd. was acquired by Irish firm Calyx in December 2006.[26] The PDP-11 software, which was owned by Mentec Inc. was then bought by XX2247 LLC, which is the owner of the software today. It is unclear if new commercial licenses are possible to buy at this time. Hobbyists can run RSX-11M (version 4.3 or earlier) and RSX-11M Plus (version 3.0 or earlier) on the SIMH emulator thanks to a free license granted in May 1998 by Mentec Inc.[27]
Legal ownership of RSX-11A, RSX-11B, RSX-11C, RSX-11D, and IAS never changed hands; therefore it passed to Compaq when it acquired Digital in 1998[28] and then to Hewlett-Packard in 2002.[29] In late 2015 Hewlett-Packard split into two separate companies (HP Inc. and Hewlett Packard Enterprise),[30] so the current owner cannot be firmly established. No new commercial licenses have been issued since at least October 1979 (RSX-11A, RSX-11B, RSX-11C)[31] or 1990 (IAS), and none of these operating systems have ever been licensed for hobbyist use.
RSX-11M-Plus also ran on PDP-11/44, PDP-11/84, PDP-11/94 (Unibus machines), as well as PDP-11/73, PDP-11/83, and PDP-11/93 (Qbus machines). One of the advantages of RSX-11M-Plus over RSX-11M was that larger programs could be created. This was achieved by having the task builder (the linker) build the program to use the separate instruction and data space feature of some PDP-11 models to put executable code and data into separate address spaces. This also allowed programs to run faster, as it reduced the need for "overlays", in which you could overlay object modules at task build time, for very large programs. Overlays were specified in a task build command file.
In 1968,[34] the Soviet Government decided that manufacturing copies of IBM mainframes[35] and DEC minicomputers,[36] [37] in cooperation with other COMECON countries,[38] was more practical than pursuing original designs. Cloning of DEC designs began in 1974, under the name of SM EVM (or). As happened with ES EVM mainframes based on the System/360 architecture, the Russians and their allies sometimes significantly modified Western designs, and therefore many SM EVM machines were binary-incompatible with DEC offerings at the time.
A clone of the RSX-11M operating system ran on the Romanian-made CORAL series family of computers (such as CORAL 2030, a clone of PDP-11).
RSX-11 was often used for general-purpose timeshare computing, even though this was the target market for the competing RSTS/E operating system. RSX-11 provided features to ensure better than a maximum necessary response time to peripheral device input (i.e. real-time processing), its original intended use. These features 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.
In order to support large programs within the PDP-11's relatively small virtual address space of 64 KB, 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 (hours to days).
The standard RSX prompt is ">" or "MCR>", (for the "Monitor Console Routine". All commands can be shortened to their first three characters when entered and correspondingly all commands are unique in their first three characters. Only the login command of "HELLO" can be executed by a user not yet logged in. "HELLO" was chosen as the login command because only the first three characters, "HEL", are relevant and this allows a non-logged in user to execute a "HELP" command.
When run on certain PDP-11 processors, each DEC operating system displays a characteristic light pattern on the processor console panel when the system is idle. These patterns are created by an idle task running at the lowest level. The RSX-11M light pattern is two sets of lights that sweep outwards to the left and right from the center of the console (inwards if the IND indirect command file processor program was currently running on older versions of RSX). By contrast, the IAS light pattern was a single bar of lights that swept leftwards. Correspondingly, a jumbled light pattern (reflecting memory fetches) is a visible indication that the computer is under load (and the idle task is not being executed). Other PDP-11 operating systems such as RSTS/E have their own distinctive patterns in the console lights.