RT-11

Source code RT-11 was written in assembly language. Heavy use of the conditional assembly and macro programming features of the MACRO-11 assembler allowed a significant degree of configurability and allowed programmers to specify high-level instructions otherwise unprovided for in machine code. RT-11 distributions included the source code of the operating system and its device drivers with all the comments removed and a program named "SYSGEN" which would build the operating system and drivers according to a user-specified configuration. Developer's documentation included a kernel listing that included comments. Device drivers In RT-11, device drivers was for producing documents. Finally, VTCOM was used to connect with and use (or transfer files to and from) another computer system over the phone via a modem. The system was complete enough to handle many modern personal computing tasks. Productivity software such as LEX-11, a word processing package, and a spreadsheet from Saturn Software, used under other PDP-11 operating systems, also ran on RT-11. Large amounts of free, user-contributed software for RT-11 were available from the Digital Equipment Computer Users Society (DECUS) including an implementation of C. Although the tools to develop and debug assembly-language programs were provided, other languages including C, Fortran, Pascal, Compatibility with other DEC operating systems Many RT-11 programs (those that did not need specialized peripherals or direct access to the hardware) could be directly executed using the RT=11 RTS (Run-time system) of the RSTS/E timesharing system or under RTEM (RT Emulator) on various releases of both RSX-11 and VMS. The implementation of DCL for RT-11 increased its compatibility with the other DEC operating systems. Although each operating system had commands and options which were unique to that operating system, there were a number of commands and command options which were common. ==Other PDP-11 operating systems==

DEC also sold RSX-11M, a multiuser, multitasking operating system with realtime features, and RSTS/E (originally named RSTS-11) a multiuser time-sharing system, but RT-11 remained the operating system of choice for data acquisition systems where real time response was required. The Unix operating system also became popular, but lacked the real-time features and extremely small size of RT-11. ==Hardware==

RT-11 ran on all members of the DEC PDP-11 family, both Q-Bus- and Unibus-based. In addition, it ran on the Professional Series and the PDT-11 "Programmed Data Terminal" systems, also from DEC. Since the PDP-11 architecture was implemented in replacement products by other companies (E.g., the M100 and family from Mentec), or as reverse-engineered clones in other countries (E.g., the DVK from the Soviet Union), RT-11 runs on these machines as well. ==Peripherals==

Adding driver support for peripherals such as a CalComp plotter, typically involved copying files, and did not require a SYSGEN. ==Compatible operating systems==

Fuzzball Fuzzball, routing software for Internet Protocols, was capable of running RT-11 programs. SHAREplus HAMMONDsoftware distributed a number of RT-11 compatible operating systems including STAReleven, an early multi-computer system and SHAREplus, a multi-process/multi-user implementation of RT-11 which borrowed some architectural concepts from the VAX/VMS operating system. RT-11 device drivers were required for operation. Transparent device access to other PDP-11s and VAX/VMS were supported with a network option. Limited RSX-11 application compatibility was also available. SHAREplus had its strongest user base in Europe. TSX-11 TSX-11, developed by S&H Computing, was a multi-user, multi-processing implementation of RT-11. The only thing it didn't do was handle the boot process, so any TSX-Plus machine was required to boot RT-11 first before running TSX-Plus as a user program. Once TSX-Plus was running, it would take over complete control of the machine from RT-11. It provided true memory protection for users from other users, provided user accounts and maintained account separation on disk volumes and implemented a superset of the RT-11 EMT programmed requests. S&H wrote the original TSX because "Spending $25K on a computer that could only support one user bugged [founder Harry Sanders]"; the outcome was the initial four-user TSX in 1976. TSX-Plus (released in 1980) was the successor to TSX, released in 1976. The system was popular in the 1980s. RT-11 programs generally ran, unmodified, under TSX-Plus and, in fact, most of the RT-11 utilities were used as-is under TSX-Plus. Device drivers generally required only slight modifications. Depending on which PDP-11 model and the amount of memory, the system could support a minimum of 12 users{{cite news ==Versions==

Variants Users could choose from variants with differing levels of support for multitasking, memory size, and separate I & D (Instruction and Data) address space: Unmapped memory • RT-11SJ (Single Job) allowed only one task. This was the initial distribution. • RT-11BL (Base-line) a stripped-down version of SJ that has minimal memory residency and lacks optional features. • RT-11FB (Foreground/Background) supported two tasks: a high-priority, non-interactive "Foreground" job, and a low-priority, interactive "Background" job. • RT-11XM (eXtended Memory), a superset of FB, provided support for memory beyond 64kb, but required a minicomputer with memory management hardware; distributed from approx. 1975-on. Up to 8 concurrent jobs. • RT-11ZB single job, supports I & D separation. • RT-11ZM provided support for systems with Separate Instruction and Data space (such as on the Unibus-based 11/44, 45, 55, 70, 84, and 94 and the Q-Bus-based 11/53, 73, 83, and 93.) Up to 8 concurrent jobs. Specialized versions Several specialized PDP-11 systems were sold based on RT-11: • LAB-11 provided an LPS-11 analog peripheral for the collection of laboratory data • PEAK-11 provided further customization for use with gas chromatographs (analyzing the peaks produced by the GC); data collection ran in RT-11's foreground process while the user's data analysis programs ran in the background. • GT4x systems added a VT11 vector graphics peripheral. Several very popular demo programs were provided with these systems including Lunar Lander and a version of Spacewar!. • GT62 systems added a VS60 vector graphics peripheral (VT11-compatible) in a credenza cabinet. • GAMMA-11 was a packaged RT-11 and PDP 11/34 system that was one of the first fully integrated Nuclear Medicine systems. It included fast analog/digital converters, 16 bit colour graphical displays, and an extensive software library for development of applications for the purpose of data collection, analysis and display from a nuclear medicine gamma camera. Clones in the USSR Several clones of RT-11 were made in the USSR: • RAFOS (РАФОС) – SM EVM • FOBOS (ФОБОС) – Elektronika 60 • FODOS (ФОДОС) • RUDOS (РУДОС) • OS DVK (ОС ДВК) – DVK • OS BK-11 (ОС БК-11) – Elektronika BK • MASTER-11 (МАСТЕР-11) – DVK • NEMIGA OS (НЕМИГА) – Nemiga PK 588 ==See also==