RSX-11

Name and origins RSX-11 began as a port to the PDP-11 architecture of the earlier RSX-15 operating system for the PDP-15 minicomputer, first released in 1971. The main architect for RSX-15 (later renamed XVM/RSX) was Dennis “Dan” Brevik. Commenting on the RSX acronym, Brevik says: to 1976, the RSX-11M project was spearheaded by noted operating system designer Dave Cutler, then at his first project. 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. as part of a broader agreement. 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. 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. 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 and then to Hewlett-Packard in 2002. In late 2015 Hewlett-Packard split into two separate companies (HP Inc. and Hewlett Packard Enterprise), with the intellectual property from DEC ending up at HPE. No new commercial licenses have been issued since at least October 1979 (RSX-11A, RSX-11B, RSX-11C) or 1990 (IAS), and none of these operating systems have ever been licensed for hobbyist use. ==Versions==

Main 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, later 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 Language), which in IAS is known by its original name, PDS (Program Development System). a computer that was never released, but RSX-11M-Plus was then used widely as a standard operating system on the PDP-11/70. :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. Hardware-specific variants • RSX-20F – Customized version of RSX-11M, to be run on PDP-11/40 front end processor operating system for the DEC KL10 processor Clones in the USSR and other Eastern Bloc countries In 1968, the Soviet Government decided that manufacturing copies of IBM mainframes in cooperation with other COMECON countries, 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. • DOS/RV, ', ОСРВM'ОСРВМ is the model of ОСРВ-СМ for the SM-1425. See:{{cite web 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). ==Operation==

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. ==See also==