RSX 11: PDP-11 Опералық Жүйелер Отбасының Тарихы

Family of computer operating systems
the operating system family

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 name suggests, RSX was designed (and commonly used) for real time use, with process control a major use. It was also popular for program development and general computing.

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 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), 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) or 1990 (IAS), 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.

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.