RT-11
Encyclopedia
RT-11 was a small, single-user real-time operating system
for the Digital Equipment Corporation
PDP-11
family of 16-bit computers. RT-11 was first implemented in 1970 and was widely used for real-time
systems, process control
, and data acquisition
across the full line of PDP-11 computers.
, but most versions could run multiple simultaneous applications. All variants of the monitors provided a Background Job. The FB, XM and ZM monitors also provided a Foreground Job, as well as six System Jobs if selected via the SYSGEN System Generation program. These tasks had fixed priorities, with the Background Job lowest and the Foreground Job highest. It was possible to switch between jobs from the system console
user interface, and SYSGEN could generate a monitor that provided a single Background Job (the SB, XB and ZB variants).
. 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.
s were built into the kernel at configuration time, but in later versions the device drivers were loadable. Because RT-11 was commonly used for device control and data acquisition, it was common for developers to write or enhance device drivers. DEC encouraged such driver development by making their hardware subsystems (from bus structure to code) open, documenting the internals of the operating system, encouraging third-party hardware and software vendors, and by fostering the development of the Digital Equipment Computer Users Society
.
, originally via a strap-selectable current-loop (for conventional teletypes) or RS-232
(later RS-422
as well) interface on one of the CPU cards; DEC also supported the VT11 and VS60 graphics display devices (vector graphics
terminal
s with a graphic character generator for displaying text, and a light pen
for graphical input). A third-party favorite was the Tektronix 4010 family.
The Keyboard Monitor (KMON) interpreted commands issued by the user and would invoke various utilities with Command String Interpreter (CSI) forms of the commands.
RT-11 command language had many features (such as commands and device names) that can be found later in DOS
line of operating systems which heavily borrowed from RT-11. The CSI form expected input and output filename
s and options ('switches' on RT-11) in a precise order and syntax. The command-line switches were separated by "/" sign rather than "-" used in Unix-like
operating systems. All commands had full form and a short one to which it could be contracted. For example, RENAME command could be contracted to REN
.
Batch files and the batch processor could be used to issue a series of commands with some rudimentary flow control
. Batch files had the extension
.BAT.
In later releases of RT-11, it was possible to invoke a series of commands using a .COM command file, but they would be executed in sequence with no flow control. Even later, it was possible to execute a series of commands with great control through use of the Indirect Command File Processor (IND), which took .CMD control files as input.
Files with the extension .SAV were a sort of executables. They were known as "save files" because the RT-11 SAVE command could be used to save the contents of memory to a disk file which could be loaded and executed at a later time, allowing any session to be saved.
The SAVE command, along with GET, START, REENTER, EXAMINE and DEPOSIT are basic commands implemented in the KMON. Some commands and utilities were later borrowed in DOS
-line of operating systems. These commands include DIR, COPY
, RENAME
, ASSIGN, CLS
, DELETE, TYPE
, HELP
and others. FORMAT command was used for physical disk formatting, although it was not capable of creating file system, for which purpose INIT command was used (analogue of DOS command FORMAT /Q). Most commands supported use of wildcards
in file names.
Physical device names were specified in the form 'dd{n}:' where 'dd' was a two-character alphabetic device name and the optional 'n' was the unit number (0–7). When the unit number is omitted, unit 0 is assumed. For example, TT: referred to the console terminal, LP: (or LP0:) referred to the parallel line printer, and DX0:, DY1:, DL4: referred to disk volumes (RX01 unit 0, RX02 unit 1, RL01 or RL02 unit 4, respectively). Logical device names consisted of 1–3 alphanumeric characters and were used in the place of a physical device name. This was accomplished using the
Later versions of RT-11 allowed specification of up to 64 units (0–77 octal) for certain devices, but the device name was still limited to three alphanumeric characters. This feature was enabled through a SYSGEN selection, and only applied to the DU and LD device handlers. In these two cases, the device name form became 'dnn:' where 'd' was 'D' for the DU device and 'L' for the LD device, and 'nn' was 00–77(octal).
and FORMAT allowed a user to manage their disk volumes. TECO
, EDIT, and the visual editor
s KED (for the DEC VT100
) and K52 (for the DEC VT52
) allowed a user to create and edit source and data files. MACRO, LINK, and LIBR allowed a user to build their own executables. ODT
, VDT and the SD device allowed a user to debug programs. DEC's version of Runoff
allowed a user to produce documents. Finally, VTCOM allowed a user to connect with and use (or transfer files to and from) another computer system over the phone using a modem.
The system was complete enough to handle many modern personal computing tasks. Large amounts of free, user-contributed software for RT-11 were available from the Digital Equipment Computer Users Society
including an implementation of C
. Although the tools to develop and debug assembly-language programs were provided, other languages including C, Fortran
, Pascal
, and several versions of BASIC
were available from DEC as "layered products" at extra cost. Versions of these and other programming languages were also available from other, third-party, sources. It is even possible to network RT-11 machines using DECNET
, the Internet
and protocols developed by other, third-party sources.
s and 56KB of memory, and could support 8 terminals. Other boot options include a 2.5MB removable hard disk platter (RK05), or magnetic tape
. Distributions were available pre-installed or on punched tape
, magnetic tape, cartridge tape, or floppy disk. A minimal but complete system supporting a single real-time user could run on a single floppy disk and in 8K 16-bit words (16KB) of RAM, including user programs. This was facilitated by support for swapping and overlaying. To realize operation on such small memory system, the keyboard command user interface would be swapped out during the execution of a user's program and then swapped into memory upon program termination. The system supported a real-time clock
, printing terminal, VT11 vector graphic unit, 16 channel 100 kHz A/D converter with 2 channel D/A, 9600 baud serial port, 16 bit bidirectional boards, etc.
employing filenames with six characters and three-character extensions ("6.3") encoded in RADIX-50
, which packed those 9 characters into only six bytes (three 16-bit words). All files were contiguous, meaning that each file occupied consecutive blocks (the minimally addressable unit of disk storage, 512 bytes) on the disk. This meant that an entire file could be read (or written) very quickly. A side effect of this file system structure was that as files were created and deleted on a volume over time, the unused disk space became fragmented and a disk would need to be periodically 'squeezed' to consolidate the unused portions (also called defragmentation
).
) 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.
, a multiuser, multitasking operating system with realtime features, and 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.
- and Unibus
-based, from the PDP-11/05 (its first target, in 1970), to the final PDP-11 implementations (PDP-11/93 and /94). 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 (Eg, the M100 and family from Mentec
), or as reverse-engineered clones in other countries (Eg, the DVK
from the Soviet Union), RT-11 runs on these machines as well.
, routing software for Internet Protocol
s, was capable of running RT-11 programs.
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.
, 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. 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.
:
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...
for the 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...
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...
family of 16-bit computers. RT-11 was first implemented in 1970 and was widely used for real-time
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
systems, process control
Process control
Process control is a statistics and engineering discipline that deals with architectures, mechanisms and algorithms for maintaining the output of a specific process within a desired range...
, and data acquisition
Data acquisition
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems typically convert analog waveforms into digital values for processing...
across the full line of PDP-11 computers.
Multitasking
RT-11 systems did not support preemptive multitaskingComputer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
, but most versions could run multiple simultaneous applications. All variants of the monitors provided a Background Job. The FB, XM and ZM monitors also provided a Foreground Job, as well as six System Jobs if selected via the SYSGEN System Generation program. These tasks had fixed priorities, with the Background Job lowest and the Foreground Job highest. It was possible to switch between jobs from the system console
System console
The system console, root console or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the kernel, from the init system and from the system logger...
user interface, and SYSGEN could generate a monitor that provided a single Background Job (the SB, XB and ZB variants).
Source code
RT-11 was written in assembly languageAssembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
. Heavy use of the conditional assembly and macro programming features of the MACRO-11
MACRO-11
MACRO-11 is an assembly language with macro facilities for PDP-11 minicomputers from Digital Equipment Corporation . It is the successor to PAL-11 , an earlier version of the PDP-11 assembly language without macro facilities....
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
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
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
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
listing that included comments.
Device drivers
In early versions of RT-11, device driverDevice driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s were built into the kernel at configuration time, but in later versions the device drivers were loadable. Because RT-11 was commonly used for device control and data acquisition, it was common for developers to write or enhance device drivers. DEC encouraged such driver development by making their hardware subsystems (from bus structure to code) open, documenting the internals of the operating system, encouraging third-party hardware and software vendors, and by fostering the development of the Digital Equipment Computer Users Society
DECUS
The Digital Equipment Computer Users' Society was an independent computer user group related to Digital Equipment Corporation.The Connect User Group Community, formed from the consolidation in May, 2008 of DECUS, Encompass, HP-Interex, and ITUG is Hewlett-Packard’s largest user community...
.
Human interface
Users generally operated RT-11 via a printing terminal or a video terminalComputer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
, originally via a strap-selectable current-loop (for conventional teletypes) or RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
(later RS-422
EIA-422
RS-422 is a technical standard that specifies electrical characteristics of a digital signalling circuit. Differential-mode signals can be sent at rates as high as 10 million bits per second, or may be sent on cables as long as 1200 metres. Some systems directly interconnect using RS 422 signals,...
as well) interface on one of the CPU cards; DEC also supported the VT11 and VS60 graphics display devices (vector graphics
Vector graphics
Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
terminal
Computer display
A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure...
s with a graphic character generator for displaying text, and a light pen
Light pen
A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy...
for graphical input). A third-party favorite was the Tektronix 4010 family.
The Keyboard Monitor (KMON) interpreted commands issued by the user and would invoke various utilities with Command String Interpreter (CSI) forms of the commands.
RT-11 command language had many features (such as commands and device names) that can be found later in DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
line of operating systems which heavily borrowed from RT-11. The CSI form expected input and output filename
Filename
The filename is metadata about a file; a string used to uniquely identify a file stored on the file system. Different file systems impose different restrictions on length and allowed characters on filenames.A filename includes one or more of these components:...
s and options ('switches' on RT-11) in a precise order and syntax. The command-line switches were separated by "/" sign rather than "-" used in Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems. All commands had full form and a short one to which it could be contracted. For example, RENAME command could be contracted to REN
Ren (command)
In computing, ren is a command in various DOS, OS/2 and Microsoft Windows command line interpreters such as COMMAND.COM, cmd.exe, 4DOS/4NT and Windows PowerShell. It is used to rename files and in some implementations also directories. It is analogous to the Unix mv command...
.
Batch files and the batch processor could be used to issue a series of commands with some rudimentary flow control
Flow control
In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...
. Batch files had the extension
Filename extension
A filename extension is a suffix to the name of a computer file applied to indicate the encoding of its contents or usage....
.BAT.
In later releases of RT-11, it was possible to invoke a series of commands using a .COM command file, but they would be executed in sequence with no flow control. Even later, it was possible to execute a series of commands with great control through use of the Indirect Command File Processor (IND), which took .CMD control files as input.
Files with the extension .SAV were a sort of executables. They were known as "save files" because the RT-11 SAVE command could be used to save the contents of memory to a disk file which could be loaded and executed at a later time, allowing any session to be saved.
The SAVE command, along with GET, START, REENTER, EXAMINE and DEPOSIT are basic commands implemented in the KMON. Some commands and utilities were later borrowed in DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
-line of operating systems. These commands include DIR, COPY
Copy (command)
In computing, copy is a command in RT-11, RSX-11, OpenVMS, DOS, OS/2 and Microsoft Windows operating systems. The command copies computer files from one directory to another. The destination defaults to the current working directory. If more than one source file is indicated, the destination must...
, RENAME
Rename
Rename is a word meaning change the name of something. Different areas, such as linguistics, relational algebra, and computer science incur renaming actions with different detailed activity, however the principles behind are all the same — change the name of something.Specific uses:* Rename...
, ASSIGN, CLS
Cls (computing)
cls is a command used by the command line interpreters COMMAND.COM and cmd.exe on DOS, OS/2 and Microsoft Windows operating systems to clear the screen or console window of commands and any output generated by them. It does not clear the user's history of commands, however...
, DELETE, TYPE
Type (command)
In computing, type is a command in various VMS. AmigaDOS, CP/M, DOS, OS/2 and Microsoft Windows command line interpreters such as COMMAND.COM, cmd.exe, 4DOS/4NT and Windows PowerShell. It is used to display the contents of specified files...
, HELP
Help (command)
In computing, help is a command in various command line shells such as COMMAND.COM, cmd.exe, 4DOS/4NT, Windows PowerShell, Bash, Singularity shell, Python and GNU Octave. It provides online information about available commands and the shell environment. It is analogous to the Unix man command...
and others. FORMAT command was used for physical disk formatting, although it was not capable of creating file system, for which purpose INIT command was used (analogue of DOS command FORMAT /Q). Most commands supported use of wildcards
Wildcard character
-Telecommunication:In telecommunications, a wildcard character is a character that may be substituted for any of a defined subset of all possible characters....
in file names.
Physical device names were specified in the form 'dd{n}:' where 'dd' was a two-character alphabetic device name and the optional 'n' was the unit number (0–7). When the unit number is omitted, unit 0 is assumed. For example, TT: referred to the console terminal, LP: (or LP0:) referred to the parallel line printer, and DX0:, DY1:, DL4: referred to disk volumes (RX01 unit 0, RX02 unit 1, RL01 or RL02 unit 4, respectively). Logical device names consisted of 1–3 alphanumeric characters and were used in the place of a physical device name. This was accomplished using the
ASSIGN command. For example, one might issue ASSIGN DL0 ABC which would cause all future references to 'ABC:' to map to 'DL0:'. Reserved logical name DK: referred to the current default device. If a device was not included in a file specification, DK: was assumed. Reserved logical name SY: referred to the system device (the device from which the system had been booted).Later versions of RT-11 allowed specification of up to 64 units (0–77 octal) for certain devices, but the device name was still limited to three alphanumeric characters. This feature was enabled through a SYSGEN selection, and only applied to the DU and LD device handlers. In these two cases, the device name form became 'dnn:' where 'd' was 'D' for the DU device and 'L' for the LD device, and 'nn' was 00–77(octal).
Software
RT-11 was distributed with utilities which allowed a user to perform many actions. The utilities DIR, DUP, PIPPeripheral Interchange Program
Peripheral Interchange Program was a utility to transfer files on and between devices on Digital Equipment Corporation's computers. It was first implemented on the PDP-6 architecture by Harrison "Dit" Morse early in the 1960s...
and FORMAT allowed a user to manage their disk volumes. TECO
Text Editor and Corrector
TECO is a text editor originally developed at the Massachusetts Institute of Technology in the 1960s, after which it was modified by 'just about everybody'...
, EDIT, and the visual editor
Visual editor
Visual editors or full screen editors are editing programs which display the text being edited on the screen as it is being edited, as opposed to line-oriented editors ....
s KED (for the DEC VT100
VT100
The VT100 is a video terminal that was made by Digital Equipment Corporation . Its detailed attributes became the de facto standard for terminal emulators.-History:...
) and K52 (for the DEC VT52
VT52
The VT52 was a CRT-based computer terminal produced by Digital Equipment Corporation introduced in September, 1975 . It provided a screen of 24 rows and 80 columns of text and supported all 95 ASCII characters as well as 32 graphics characters. It supported asynchronous communication at baud rates...
) allowed a user to create and edit source and data files. MACRO, LINK, and LIBR allowed a user to build their own executables. ODT
Octal Debugging Technique
On-line Debugging Tool, or ODT, was the name of several debugger programs originally developed for DEC hardware. Various operating systems including OS/8, RT-11, RSX-11, and RSTS/E implemented ODT as did the firmware console of all of the LSI-11-family processors including the 11/03, 11/23/24,...
, VDT and the SD device allowed a user to debug programs. DEC's version of Runoff
Runoff (program)
runoff was the text formatting program on the Multics operating system.It was a descendant of the RUNOFF type-setting program from CTSS and was originally written by Jerome H. Saltzer...
allowed a user to produce documents. Finally, VTCOM allowed a user to connect with and use (or transfer files to and from) another computer system over the phone using a modem.
The system was complete enough to handle many modern personal computing tasks. Large amounts of free, user-contributed software for RT-11 were available from the Digital Equipment Computer Users Society
DECUS
The Digital Equipment Computer Users' Society was an independent computer user group related to Digital Equipment Corporation.The Connect User Group Community, formed from the consolidation in May, 2008 of DECUS, Encompass, HP-Interex, and ITUG is Hewlett-Packard’s largest user community...
including an implementation of C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
. Although the tools to develop and debug assembly-language programs were provided, other languages including C, Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
, Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
, and several versions of BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
were available from DEC as "layered products" at extra cost. Versions of these and other programming languages were also available from other, third-party, sources. It is even possible to network RT-11 machines using DECNET
DECnet
DECnet is a suite of network protocols created by Digital Equipment Corporation, originally released in 1975 in order to connect two PDP-11 minicomputers. It evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s...
, the Internet
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
and protocols developed by other, third-party sources.
Distributions and Minimal system configuration
The RT-11 operating system could be booted from, and perform useful work on, a machine consisting of two 8-inch 250KB floppy diskFloppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
s and 56KB of memory, and could support 8 terminals. Other boot options include a 2.5MB removable hard disk platter (RK05), or magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
. Distributions were available pre-installed or on punched tape
Punched tape
Punched tape or paper tape is an obsolete form of data storage, consisting of a long strip of paper in which holes are punched to store data...
, magnetic tape, cartridge tape, or floppy disk. A minimal but complete system supporting a single real-time user could run on a single floppy disk and in 8K 16-bit words (16KB) of RAM, including user programs. This was facilitated by support for swapping and overlaying. To realize operation on such small memory system, the keyboard command user interface would be swapped out during the execution of a user's program and then swapped into memory upon program termination. The system supported a real-time clock
Real-time clock
A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.-Terminology:The term is used to avoid...
, printing terminal, VT11 vector graphic unit, 16 channel 100 kHz A/D converter with 2 channel D/A, 9600 baud serial port, 16 bit bidirectional boards, etc.
File system
RT-11 implemented a simple and fast file systemFile system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
employing filenames with six characters and three-character extensions ("6.3") encoded in RADIX-50
RADIX-50
RADIX-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...
, which packed those 9 characters into only six bytes (three 16-bit words). All files were contiguous, meaning that each file occupied consecutive blocks (the minimally addressable unit of disk storage, 512 bytes) on the disk. This meant that an entire file could be read (or written) very quickly. A side effect of this file system structure was that as files were created and deleted on a volume over time, the unused disk space became fragmented and a disk would need to be periodically 'squeezed' to consolidate the unused portions (also called defragmentation
Defragmentation
In the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
).
Compatibility with other DEC operating systems
Many RT11 programs (those that did not need specialized peripherals or direct access to the hardware) could be directly executed using the RT11 RTS (Run-time systemRun-time system
A run-time system is a software component designed to support the execution of computer programs written in some computer language...
) of the RSTS/E
RSTS/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...
timesharing system or under RTEM (RT Emulator) on various releases of both RSX-11 and VMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
.
The implementation of DCL
DIGITAL Command Language
DCL, the DIGITAL Command Language, is the standard command languageadopted by most of the operating systems that were sold by the former Digital Equipment Corporation...
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-11RSX-11
RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
, a multiuser, multitasking operating system with realtime features, and RSTS-11
RSTS/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...
a multiuser time-sharing system, but RT-11 remained the operating system of choice for data acquisition
Data acquisition
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems typically convert analog waveforms into digital values for processing...
systems where real time response was required. The Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
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-BusQ-Bus
The Q-bus was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts....
- and Unibus
Unibus
The Unibus was the earliest of several computer bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.-History:...
-based, from the PDP-11/05 (its first target, in 1970), to the final PDP-11 implementations (PDP-11/93 and /94). 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 (Eg, the M100 and family from Mentec
Mentec PDP-11
Mentec Limited was founded in 1978 and initially focused on the development of monitoring and control software and systems. It was a significant Digital reseller and OEM in Ireland....
), or as reverse-engineered clones in other countries (Eg, the DVK
DVK
DVK is a Soviet PDP-11-compatible personal computer.The design is also known as Elektronika MS-0501 and Elektronika MS-0502.Earlier models of DVK series were based on K1801VM1 or K1801VM2 microprocessors with 16 bit address bus. In the later models, the KM1801VM3 microprocessor was used.-...
from the Soviet Union), RT-11 runs on these machines as well.
Fuzzball
FuzzballFuzzball router
Fuzzball routers were the first modern routers on the Internet. They were DEC LSI-11 computers loaded with the Fuzzball software written by David L. Mills . The name "Fuzzball" was the colloquialism for Mills' routing software. Six provided the routing backbone of the first 56 kbit/s NSFnet,...
, routing software for Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
s, 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/VMSOpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
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
RSX-11
RSX-11 is a family of real-time operating systems mainly for PDP-11 computers created by Digital Equipment Corporation , common in the late 1970s and early 1980s. RSX-11D first appeared on the PDP-11/40 in 1972...
application compatibility was also available. SHAREplus had its strongest user base in Europe.
TSX-11
S&H Computing developed and distributed TSX-PlusTSX-Plus
TSX-Plus is a multi-user operating system for the PDP-11/LSI-11 series of computers. It was developed by S&H Computer Systems, Inc. and is based on DEC's RT-11 single-user real-time operating system...
, 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. 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.
Release history
| Version | Release date | Notes |
|---|---|---|
| RT-11 | July 1973 | |
| RT-11 v2 | 1974 | |
| RT-11 v2C | 1976 | |
| RT-11 v3 | February 1977 | Morris, D |
| RT-11 4 | 21 February 1980 | |
| GAMMA-11 | 1980? | |
| RT-11 5.0.3 | Late 1982? | |
| RT-11 5.1 | 1984 | |
| RT-11 5.2 | 1985 | |
| RT-11 5.3 | 1986 | |
| RT-11 5.4 | August 1986? | |
| RT-11 5.5 | ? | |
| RT-11 5.6 | October 1992? | |
| RT-11 5.7 | 29 October 1998 |
Variants
Users could choose from four variants with differing levels of support for multitaskingComputer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
:
- RT-11SJ (Single Job) allowed only one task. This was the initial distribution.
- 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) provided support for memory beyond 64kb, but required a minicomputer with memory management hardware; distributed from approx. 1975-on.
- RT-11ZM provided support for systems with Separate Instruction and Data space (such as on the UnibusUnibusThe Unibus was the earliest of several computer bus technologies used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.-History:...
-based 11/44, 45, 55, 70, 84, and 94 and the Q-BusQ-BusThe Q-bus was one of several bus technologies used with PDP and MicroVAX computer systems manufactured by the Digital Equipment Corporation of Maynard, Massachusetts....
-based 11/53, 73PDP-11/73The PDP-11/73 was the third generation of the PDP-11 series of 16-bit minicomputers produced by Digital Equipment Corporation to use LSI processors...
, 83, and 93)
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 RT11'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 LanderLunar LanderLunar Lander is the name of several video games. In all variations of the game, the player must portion a limited amount of fuel to land on the moon without crashing...
and a version of Spacewar!. - 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 medicineNuclear medicineIn nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
gamma cameraGamma cameraA gamma camera, also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy...
.
Clones in the USSR
Several clones of RT-11 were made in the USSR:- RAFOS ("РАФОС") — SM EVMSM EVMSM EVM was the general name for several types of Soviet and Comecon minicomputers produced in the 1970s and 1980s. Production began in 1975....
- FOBOS ("ФОБОС") — Elektronika 60
- FODOS ("ФОДОС")
- RUDOS ("РУДОС")
- OS DVK ("ОС ДВК") — DVKDVKDVK is a Soviet PDP-11-compatible personal computer.The design is also known as Elektronika MS-0501 and Elektronika MS-0502.Earlier models of DVK series were based on K1801VM1 or K1801VM2 microprocessors with 16 bit address bus. In the later models, the KM1801VM3 microprocessor was used.-...
- OS BK-11 ("ОС ВК-11") — Elektronika BKElektronika BKThe Elektronika BK was a series of 16-bit PDP-11-compatible Soviet home computers developed by NPO Scientific Center, the leading Soviet microcomputer design team at the time. It was also responsible for the more powerful UKNC and DVK micros...
- MASTER-11 ("МАСТЕР-11") — DVKDVKDVK is a Soviet PDP-11-compatible personal computer.The design is also known as Elektronika MS-0501 and Elektronika MS-0502.Earlier models of DVK series were based on K1801VM1 or K1801VM2 microprocessors with 16 bit address bus. In the later models, the KM1801VM3 microprocessor was used.-...