View source for RSTS/E

{{Short description|Computer operating system}}
{{Infobox OS
|name = RSTS
|logo = [[File:Rsts Spike.png|150px]]
|screenshot = [[File:Rstse-10 1.png|300px]]
|caption = RSTS/E 10.1, running the DCL CLI
|developer = [[Digital Equipment Corporation]], later [[Mentec International Ltd|Mentec]]
|source_model = [[Closed source]]<ref>{{Cite web|url=http://bitsavers.org/bits/DEC/pdp11/rsts/|title = Index of /Bits/DEC/Pdp11/RSTS}}</ref>
|kernel_type = [[Time-sharing]] [[operating system]]s
|supported_platforms = [[PDP-11]]
|ui = [[Command-line interface]]: [[DIGITAL Command Language|DCL (Digital Command Language)]]
|released = {{Start date and age|1970}}
|latest_release_version = RSTS V10.1
|latest_release_date = {{Start date and age|1992}}<ref>{{cite web
|url=http://www.computinghistory.org.uk/det/40734/Mentec-RSTS-E-Version-10-1-Release-Notes
|title=Mentec - RSTS/E Version 10.1 Internals and Data Structures Manual
|access-date=November 7, 2017}}</ref>
|marketing_target =
|language = [[English language|English]]
|programmed_in = [[MACRO-11]] [[assembly language]], [[BASIC-PLUS]]-2, [[DIGITAL Command Language|DCL]]
|prog_language = [[ALGOL|ALGOL-60]], [[APL (programming language)|APL]], [[BASIC-PLUS]], BASIC-PLUS-2, [[C (programming language)|C]], [[COBOL]], [[DATATRIEVE]], [[DIBOL]], [[Forth (programming language)|Forth]], [[Fortran]], [[MACRO-11]], [[Pascal (programming language)|Pascal]], [[IBM RPG|RPG II]], [[TECO (text editor)|TECO]]
|updatemodel = Binary patches, complete binaries
|package_manager = BACKUP
|working_state = No development, still available
|license = [[Proprietary software|Proprietary]]
|preceded by = [[TSS/8]]
|succeeded by = 
|website =
}}
'''RSTS''' ({{IPAc-en|ˈ|r|ᵻ|s|t|ᵻ|s}}) is a [[multi-user]] [[time-sharing]] [[operating system]] developed by [[Digital Equipment Corporation]] (DEC, now part of [[Hewlett-Packard]]) for the [[PDP-11]] series of [[16-bit]] [[minicomputer]]s. The first version of RSTS (RSTS-11, [[#Versions|Version 1]]) was implemented in 1970 by DEC [[Software engineering|software engineers]] that developed the [[TSS-8]] time-sharing operating system for the [[PDP-8]]. The last version of RSTS (RSTS/E, [[#Versions|Version 10.1]]) was released in September 1992. RSTS-11 and RSTS/E are usually referred to just as "RSTS" and this article will generally use the shorter form. RSTS-11 supports the BASIC programming language, an extended version called BASIC-PLUS, developed under contract by ''Evans Griffiths & Hart'' of Boston.<ref name="EGH.HC83">{{cite magazine |author=Fleig |first=Clare P. |date=March 1983 |title=Evans, Griffiths & Hart |magazine=Hardcopy |pages=51–54}}</ref><ref>{{cite web|title=EGH Company History|url=http://www.egh.com/about/history.htm}}</ref> Starting with RSTS/E version 5B, DEC added support for additional programming languages by emulating the execution environment of the [[RT-11]] and [[RSX-11]] operating systems.

==Acronyms and abbreviations==
{{Div col}}
*'''BTSS''' (Basic Time Sharing System – never marketed) – The first name for RSTS.<ref>{{Cite web|url=http://elvira.stacken.kth.se/rsts/rsts_80th_birthday.html|title=RSTS 80th Birthday}}</ref>
*'''CCL''' ([[Concise Command Language]]) – equivalent to a command to run a program kept in the [[command-line interpreter|Command Line Interpreter]].
*'''CIL''' (Core Image Library) – A container file format used to hold one or more standalone (bootable) programs and operating systems, such as RSTS through version 6A.
*'''CILUS''' (Core Image Library Update and Save) – [[DOS-11]] program to manipulate a CIL file.<ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |date=January 1973 |title=RSTS-11 System Manager Guide |url=https://archive.org/details/bitsavers_decpdp11rsTSmgr73_10840398 |location=Maynard, MA |publisher=Digital Equipment Corporation}}</ref>
*'''CLI''' (Command Line Interpreter) – See [[Command-line interface]].
*'''CUSPs''' (Commonly Used System Programs) – System management applications like [[Task Manager]] or [[Registry Editor]] on  [[Microsoft Windows]].<ref>{{cite web |url=ftp://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/rsts/V07.2/AA-5246E-TC_RSTS_E_V7.2_Release_Notes_Jun82.pdf |archive-url=https://web.archive.org/web/20200129000704/http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/rsts/V07.2/AA-5246E-TC_RSTS_E_V7.2_Release_Notes_Jun82.pdf |archive-date=2020-01-29 |url-status=dead |title=FTP link |work=bitsavers.informatik.uni-stuttgart.de }}</ref>  On RSTS-11, CUSPs were written in BASIC-Plus just like user programs.
*'''DCL''' (Digital Command Language) – See [[DIGITAL Command Language]].
*'''DTR''' (DATATRIEVE) – programming language
*'''FIP''' (File Information Processing) – resident area for issuing file requests
*'''FIRQB''' (File Information Request Queue Block) – A data structure containing information about file requests.<ref>{{cite web |url=ftp://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/rsts/V09/7_MACRO_Programming/AA-EZ10A-TC_RSTS_E_V9.0_System_Directives_Manual_Jun85.pdf |archive-url=https://web.archive.org/web/20200129110034/http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/rsts/V09/7_MACRO_Programming/AA-EZ10A-TC_RSTS_E_V9.0_System_Directives_Manual_Jun85.pdf |archive-date=2020-01-29 |url-status=dead |title=FTP link |work=bitsavers.informatik.uni-stuttgart.de }}</ref>
*'''KBM''' (Keyboard Monitor) – Analogous to Command Line Interpreter.
*'''LAT''' (Local Area Transport) – Digital's predecessor to [[Internet protocol suite|TCP/IP]]
*'''MFD''' (Master File Directory) – [[Root directory]] of file system.<ref name="bitsavers.informatik.uni-stuttgart.de">{{cite book |author=<!--Staff writer(s); no by-line.--> |date=July 1989 |title=RSTS/E System Manager Guide |url=http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp11/rsts/V09/2_System_Mangement/AA-2762G-TC_RSTS_E_V9.7_System_Managers_Guide_Jul89.pdf |location=Maynard, MA |publisher=Digital Equipment Corporation}}</ref>
*'''PBS''' (Print Batch Services)
*'''PIP''' ([[Peripheral Interchange Program]])
*'''PPN''' (Project Programmer Number) – Analogous to [[group identifier|GID]] and [[user identifier|UID]] in Unix.
*'''RDC''' (Remote Diagnostics Console) – A replacement front panel for a PDP-11 which used a serial connection to the console terminal or a modem instead of lights and toggle switches to control the CPU.
*'''RSTS-11''' (Resource Sharing Time Sharing System) – The first commercial product name for RSTS
*'''RSTS/E''' (Resource Sharing Timesharing System Extended) – The current implementation of RSTS.
*'''RTS''' (Run Time System) – Read only segment of code provided by the supplier which would be mapped into the high end of a 32K, 16-bit [[Word (computer architecture)|word]] address space that a user program would use to interface with the operating system. Only one copy of an RTS would be loaded into RAM, but would be mapped into the address space of any user program that required it. In essence, shared, re-entrant code, to reduce RAM requirements, by sharing the code between any programs that required it.
*'''RTSS''' (Resource Time Sharing System – never marketed) – The second name for RSTS
*'''SATT''' (Storage Allocation Truth Table) a series of 512KB blocks on every disk that indicated if the block, or cluster, on the whole disk was allocated on the disk. Bitwise, a 1 indicated a cluster was in use; a 0 indicated it was not in use.
*'''SIL''' (Save Image Library) – The OS container file format after the RSTS system generation procedure was switched from one using DOS-11 to one running natively on RSTS/E, called that by analogy to the CIL it replaced.
*'''SILUS''' (Save Image Library Update and Save) – The program to create SIL files, called that by analogy to the (unrelated) DOS-11 CILUS program it replaced.
*'''UFD''' (User File Directory) – A user's [[home directory]]. Root directory of a file system.<ref name="bitsavers.informatik.uni-stuttgart.de"/>
*'''XRB''' (Transfer Request Block) – A data structure containing information about other types of system requests that do not use FIRQBs to convey the information
{{Div col end}}

==Development==

===1970s===
The [[kernel (operating system)|kernel]] of RSTS was [[computer programming|programmed]] in the [[assembly language]] [[MACRO-11]], [[compiler|compiled]] and [[installation (computer programs)|installed]] to a [[hard disk drive|disk]] using the '''[[DOS-11|CILUS]]''' [[computer program|program]], running on a [[DOS-11]] operating system. RSTS [[booting|booted]] into an extended version of the [[BASIC]] programming language which DEC called "[[BASIC-PLUS]]". All of the [[system software]] '''CUSPS''' for the operating system, including the programs for resource accounting, [[login]], logout, and managing the system, were written in BASIC-PLUS. From 1970 to 1973, RSTS ran in only [[kilobyte|56K bytes]] of [[magnetic core memory]] (64 kilobytes including the [[memory-mapped I/O]] space). This would allow a system to have up to 16 [[computer terminal|terminal]]s with a maximum of 17 [[Job (computing)|jobs]]. The maximum program size was 16K bytes.<ref name="PeterDickAddendum">Dick, P: "The History of RSTS: An Addendum", page 25. "The VAX/RSTS Professional Magazine" February 1, 1984, Vol 6, No 1, ISSN 0746-1909</ref> By the end of 1973 DEC estimated there were 150 [[license]]d systems running RSTS.<ref name="PeterDick">Dick, P.: "The History of RSTS", pp. 24–26. "The RSTS Professional Magazine" June 1, 1983, Vol 5, No 3, ISSN 0745-2888</ref>

In 1973, [[memory management]] support was included in RSTS (now RSTS/E) for the newer DEC [[PDP-11/40]] and [[PDP-11/45]] minicomputers (the [[PDP-11/20]] was only supported under RSTS-11). The introduction of memory management in the newer PDP-11 computers not only meant these machines were able to address four times the amount of memory (18-bit [[address space|addressing]], 256K bytes), it also paved the way for the developers to separate [[user space|user mode]] processes from the core of the kernel.

In 1975, memory management support was again updated for the newer 22-bit addressable [[PDP-11/70]]. RSTS systems could now be expanded to use as much as two [[megabyte]]s of memory running up to 63 jobs. The '''[[run-time system|RTS]]''' and '''[[Concise Command Language|CCL]]''' concepts were introduced although they had to be compiled in during "[[System generation|SYSGEN]]". Multi-terminal service was introduced which would allow a single job the ability to control multiple terminals (128 total). Large-message send/receive and interprocess communication became very sophisticated and efficient. By August there are 1,200 licensed systems.<ref name="PeterDick"/>

In 1977, the installation process for RSTS was no longer dependent on DOS-11. The RSTS kernel could now be compiled under the [[RT-11]] '''RTS''', formatted as a kernel file with RT-11 '''SILUS''', and [[Copying|copied]] to the system or other disks, while the [[computer]] was time-sharing. The BASIC-PLUS '''RTS''' (as well as RT-11, [[RSX-11]], [[TECO (text editor)|TECO]] and third party '''RTS'''s) all ran as user mode processes, independent of the RSTS kernel. A [[system administrator|systems manager]] could now decide during the bootstrap phase which '''RTS''' to run as the systems default Keyboard Monitor ('''[[command line interpreter|KBM]])'''. By now, there were some 3,100 licensed systems.<ref name="PeterDick"/>

In 1978, the final memory management update was included for all machines that could support 22-bit addressing. RSTS could now use the maximum amount of memory available to a PDP-11 (4 megabytes). Support was also included for SUPERVISORY mode which made RSTS the first DEC operating system with this capability. [[DECnet]] was also supported as well as remote diagnostics from field service technicians at the '''RDC''' in [[Colorado Springs, Colorado]] (a DEC subscription service). By the end of the [[decade]], there are over 5,000 licensed systems.<ref name="PeterDick"/>

===1980s===
In 1981, support for separate instruction and data space for users with [[Unibus]] machines ([[PDP-11/44]], PDP-11/45, PDP-11/55 and PDP-11/70) provided an extension to the memory constraints of an individual program. Compiling programs to use separate instruction and data space would soon give a program up to 64&nbsp;KB for instructions, and up to 64&nbsp;KB for buffering data. The '''[[DIGITAL Command Language|DCL]]''' RTS was included as well as support for the newer revision of DECnet III.

By 1983, with an estimated 15,000 DEC machines running RSTS/E,<ref name=EGH.HC83/> V8.0-06 included support for the smallest 18-bit PDP-11 sold by DEC (the MicroPDP-11). A pre-generated kernel and '''CUSPS''' were included in this distribution to make installation on the MicroPDP-11 easier. DEC sold the pre-generated version on the MicroPDP-11 as MicroRSTS at a reduced price, however users needed to purchase the full version if they had a need to generate their own kernel. The file system was upgraded and given the designation RSTS Directory Structure 1 (RDS1).<ref>[http://www.rsts.org/internals/mayfieldRSTS8internals.pdf Mayfield, M: "RSTS/E Monitor Internals", pages 1–9.]</ref> All previous versions of the RSTS file system are given the designation RDS0.<ref>[http://www.rsts.org/internals/mayfieldRSTS8internals.pdf Mayfield, M.: "RSTS/E Monitor Internals", pages 1–4.]</ref> The newer file system was designed to support more than 1700 user accounts.<ref name="CarlMarbach">Marbach, C.: "RSTS and the Micro-11", p. 50. "The VAX/RSTS Professional Magazine" August 1, 1983, Vol 5, No 4, ISSN 0745-2888</ref> "It is now thought that there are well over 10,000 licensed users and at least an equal number of unlicensed users!".<ref name="PeterDick"/>

From 1985 to 1989, RSTS became a mature product in the [[#Versions|Version 9]] revisions. '''DCL''' was installed as the primary '''RTS''' and the file system was again upgraded (now RDS1.2) to support new user account features. Passwords were encrypted using a modified DES [[algorithm]] instead of limited to six (6) characters stored in [[DEC Radix-50]] format. Before Version 9, there was a non-user system account in the project (group) zero (the designation is [0,1]), and all accounts in project number 1 were privileged (not unlike the [[root account]] on [[Unix]] systems). With the release of Version 9, additional accounts could be created for project zero, and multiple privileges could be individually set for any account. Support for the '''[[Local Area Transport|LAT]]''' protocol was included, as well as the ability to run the newest version of DECnet IV. These network enhancements give any user connected to a terminal through a [[DECserver]] the ability to communicate with a RSTS machine, just as easily as with a [[VAX]] running [[OpenVMS|VMS]]. The '''DCL''' command structure between DEC operating systems also contributed to the familiar look and feel:

<blockquote>This is not just another pseudo command file processor; it is based on VMS features. The DCL command file processor is fully supported and integrated in RSTS through extensive changes to DCL and the monitor. DCL executes command files as part of your job; therefore, no pseudo keyboard or forcing of commands to your keyboard is necessary (as with ATPK).<ref>Romanello, G.: "A Preview of RSTS/E Version 9.0", p. 28. "The VAX/RSTS Professional Magazine" December 1, 1984, Vol 6, No 6, ISSN 0746-1909</ref></blockquote>

===1990s===
In 1994, DEC sold most of its PDP-11 software business to [[Mentec International Ltd|Mentec]].<ref>{{cite web|url=http://www.mentec-inc.com/ |title=PDP-11 RSX RT RSTS Emulator Osprey Charon |date=August 13, 2006 |work=archive.org |access-date=December 26, 2016 |archive-url=https://web.archive.org/web/20060813131029/http://www.mentec-inc.com/ |archive-date=August 13, 2006 }}</ref> Digital continued to support its own PDP-11 customers for a short period after with the assistance of Mentec staff.

In 1997, Digital and Mentec granted anyone wishing to use RSTS 9.6 or earlier for non-commercial, hobby purposes no-cost license. The license is only valid on the [[SIMH]] PDP-11 emulator. The license also covers some other Digital operating systems. Copies of the license are included in an authorized software kit available for download on the official website of the [[SIMH]] emulator.<ref>See for example this image of RSTS/E 7.0 installation tapes: http://simh.trailing-edge.com/kits/rstsv7gen.tar.Z</ref>

==Documentation==
The standard complement of documentation manuals that accompanies a RSTS distribution consists of at least 11 large three-ring binders (collectively known as "The orange wall"), one small three-ring binder containing the RSTS/E Quick Reference Guide and a paperback copy of ''Introduction to BASIC AA-0155B-TK''. Each of the 11 three-ring binders contains:

[[File:RSTS Docs.jpg|thumb|right|upright=1.4|Example of a RSTS/E document shelf]]

Volume 1: General Information and Installation
*Documentation Directory
*Release Notes
*Maintenance Notebook
*System Installation and Update Guide

Volume 2: System Management
*System Manager's Guide

Volume 3: System Usage
*System User's Guide
*Guide to Writing Command Procedures

Volume 4: Utilities
*Utilities Reference Manual
*Introduction to the EDT Editor
*SORT/MERGE User's Guide
*RUNOFF User's Guide

Volume 4A: Utilities
*EDT Editor Manual

<!-- Deleted image removed: [[File:MicroPDP-11 53wRSTSDocs.jpg|thumb|right|upright=1.4|MicroPDP-11/53 with various RSTS/E Documents]] -->
Volume 4B: Utilities
*Task Builder Reference Manual
*Programmer's Utilities Manual
*RT11 Utilities Manual
*TECO User's Guide

Volume 5: BASIC-PLUS
*BASIC-PLUS Language Manual

Volume 6: System Programming
*Programming Manual

Volume 7: MACRO Programming
*System Directives Manual
*ODT Reference Manual

Volume 7A: MACRO Programming
*MACRO-11 Language Manual
*RMS-11 MACRO Programmer's Guide

Volume 8: RMS [<nowiki/>[[Record Management Services]]]
*RMS-11: An Introduction
*RMS11 User's Guide
*RMS-11 Utilities

==Operation==

===Communication===
RSTS uses a [[serial communication]] connection to interact with the operator. The connection might be a local [[computer terminal]] with a 20&nbsp;[[ampere|mA]] [[current loop]] interface, an [[RS-232]] interface (either local [[serial port]] or remote connection via [[modem]]), or by an [[Ethernet]] connection using DECnet or LAT. As many as 128 terminals (using multi-terminal service) can connect to a RSTS system, running a maximum of 63 jobs (depending on the [[Central processing unit|processor]] being used, the amount of memory and disk space, and the [[system load]]). Most RSTS systems had far fewer terminals. Users can also submit jobs to be run in [[batch file|batch]] mode. There is also a batch program called "ATPK" that allows users to run a series of commands on an imaginary terminal (pseudo-terminal) in semi-interactive mode similar to batch commands in [[MS-DOS]].

===Login [Project, Programmer]===
Users connect to the system by typing the [[login|LOGIN]] command (or HELLO) at a logged-out terminal and pressing return. Typing any command at a logged-out terminal starts the LOGIN program which then interprets the command. If it is one of the commands which were allowed to be used by a user that is not yet logged in ("Logged Out"), then the associated program for that command is CHAINed, otherwise the message "Please say HELLO" is printed on the terminal. Prior to Version 9, a user can also initiate a 1 line login, however this leaves the user's password on the screen for anyone else in the room to view (examples follow):

[[File:rsts.png|thumb|right|upright=1.4|RSTS/E login and logout with BASIC as default RTS]]

<pre>
Bye

HELLO 1,1;SECRET

Ready
</pre>

or

<pre>
I 1,1;SECRET

Ready
</pre>

or

<pre>
LOGIN 1,1;SECRET

Ready
</pre>

The status of a terminal can be determined from the command responses, printed by the command interpreter. A logged-in user communicating with the BASIC-PLUS '''KBM''' (key board monitor) is given the prompt "Ready" and a user who is logged out is given the prompt "Bye".

A user logs in by supplying their '''PPN''' number and password. User numbers consist of a project number (equivalent to a [[Group (computing)|group number]] in Unix), a comma, and a programmer number. Both numbers are in the range of 0 to 254, with special exceptions. When specifying an account, the project and programmer number are enclosed in brackets. A typical user number can be [10,5] (project 10, programmer 5), [2,146], [254,31], or [200,220], etc. When a user is running a system program while logged out (because the system manager has enabled it) their '''PPN''' number is [0,0], and appears in the SYSTAT '''CUSP''' as **,**. Thus that is not a valid account number. If the user specifies a slash (/) instead of a comma between the project number and programmer number, a system wide message stored in [1,2]NOTICE.TXT (equivalent to the Unix [[message of the day|motd]]) will not be displayed at login.

===System and user accounts===
In every project, the programmer number 0 is usually reserved to as a group account, as it can be referenced by the special symbol #. If one's user number is [20,103], a reference to a file name beginning with "#" refers to a file stored in the account of the user number [20,0]. This feature is useful in educational environments, as programmer number 0 can be issued to the instructor of a class, and the individual students given accounts with the same project number, and the instructor can store in his account files marked as shared only for that project number (which would be students in that class only, and no other).

Two special classes of project numbers exist. The project number 0 is generally reserved for system software, and prior to Version 9 there is only 1 project 0 account (named [0,1]). Programmers in the project number 1 are privileged accounts, equivalent to the single account "root" on Unix systems, except that the account numbers [1,0] through [1,254] are all privileged accounts. As of Version 9, any account can be granted specific privileges by the systems manager.

The account [0,1] is used to store the operating system file itself, all run-time [[Library (computing)|library]] systems, and certain system files relating to booting the system (author's comments appear on the right in bold):

 DIR [0,1]
  Name .Ext    Size   Prot    Date       SY:[0,1]
 BADB  .SYS       0P  < 63> 06-Jun-98         '''List of bad blocks'''
 SATT  .SYS       3CP < 63> 06-Jun-98         '''Bitmap of allocated disk storage'''
 INIT  .SYS     419P  < 40> 06-Jun-98         '''[[boot loader|Operating system loader program]]'''
 ERR   .ERR      16CP < 40> 06-Jun-98         '''System error messages'''
 RSTS  .SIL     307CP < 60> 06-Jun-98         '''Operating system itself'''
 BASIC .RTS      73CP < 60> 06-Jun-98         '''BASIC-PLUS run time system'''
 RT11  .RTS      20C  < 60> 06-Jun-98         '''RT-11 run time system'''
 SWAP  .SYS    1024CP < 63> 06-Jun-98         '''System [[swap file]]'''
 CRASH .SYS      35CP < 63> 06-Jun-98         '''[[core dump|System crash dump]]'''
 RSX   .RTS      16C  < 60> 23-Sep-79         '''RSX-11 run-time system'''
 TECO  .RTS      39C  < 60> 24-Sep-79         '''TECO text editor'''
 
 Total of 1952 blocks in 11 files in SY:[0,1]
 
 (''Editor's note: This directory listing is prior to Version 9.'')

The '''DIR''' command is an installed CCL equivalent to a RUN command for the DIRECT program. [0,1] is the account number (and directory name) of the operating system storage account. It would be referred to as "project number 0, programmer number 1".

The numbers shown after each file represent its size in disk blocks, a block being 512 [[byte]]s or 1/2 kilobyte (K). "C" indicates the file is contiguous (is stored as one file without being separated into pieces, similar to files on a [[Microsoft Windows]] system after a drive has been [[defragmentation|defragmented]]), while "P" indicates it is specially protected (cannot be deleted, even by a privileged user, unless the P bit is cleared by separate command). The numbers in brackets (like "< 40>") represent the protections for the file, which is always displayed in decimal. Protections indicate if the file may be seen by any other user, by other users with the same programmer number, if the file is read only or if it may be altered by another user, and whether the file may be executed by an ordinary user giving them additional privileges. These protection codes are very similar to the [[File-system permissions|r, w and x protections]] in [[Unix]] and similar operating systems such as [[BSD]] and [[Linux]]. Code 60 is equivalent to a private file, code 63 is a private non-deletable file, and 40 is a public file.

Library files are kept in account [1,1] and it is usually referenced by the logical name LB:. The account [1,2] is the system startup account (much like a Unix system starting up under root), and contains the system '''CUSPS''' that could be referenced by prefixing the '''CUSP''' name with a dollar sign ($). "!" is used for account [1,3], "%" for [1,4] and "&amp;" for [1,5]. The account [1,1] also had the special privilege of being the only account where a user logged in under that account is permitted to execute the [[PEEK and POKE|POKE]] system call to put values into any memory in the system. Thus the account number [1,1] is the closest equivalent to "root" on Unix-based systems.

==Run-time environments==
One of the features of RSTS is the means for the execution of programs and the environment used to run them. The various environments allowed for programming in BASIC-PLUS, the enhanced and hard compiled BASIC-Plus-2, and in more traditional programming languages such as [[COBOL]] (eventually upgraded to COBOL-85) and [[FORTRAN]] IV (eventually upgraded to FORTRAN-77). Other languages were supported such as [[DIBOL]] and [[MUMPS]]. These environments were separate from each other such that one could start a program from one environment and the system would switch to a different environment while running a different program, and then return the user to the original environment they started with. These environments were referred to as a Runtime System (''RTS)''. The term for the [[command line interface]] that most of these RTSs had was the ''KBM''. Prior to Version 9, the systems manager needed to define which RTS the system would start under, and it had to be one that would execute compiled programs.

A systems manager may also install special '''CCL''' (concise command language) commands, which take precedence over all KBM commands (with the exception of '''DCL'''). A CCL is analogous to a shortcut to a program on a Windows system or a [[symbolic link]] on Unix-based systems. CCLs are installed as a [[memory resident|memory-resident]] command either during startup, or dynamically while the system is running by a system's manager (i.e.: it is not permanent like a disk file).

When logged in, a user can "SWITCH" to any of these environments, type language statements in the BASIC-PLUS programming language, issue RUN commands to specific programs, or issue a special command called a '''CCL''' to execute a program with command options.

Most RSTS systems managers generated the kernel to include the "Control-T" one line status option which could tell the user what program they were running, under what '''RTS''' the program was using, how much memory the program was taking, how much it could expand to, and how much memory the '''RTS''' was using.

===BASIC-PLUS===
Programs written in [[BASIC-PLUS]] ran under the BASIC '''RTS''', which allowed them up to 32K bytes of memory (out of 64K total). The language was interpreted, each different keyword being internally converted to a unique [[byte code]] and the variables and data being indexed and stored separately within the memory space. The internal byte-code format was known as PCODE. When the interactive SAVE command was issued, the BASIC Plus '''RTS''' simply saved the working memory area to a disk file with a ".BAC" extension. Although this format was undocumented, two Electronic Engineering undergraduates from [[Southampton University]] in the UK (Nick de Smith and David Garrod) developed a [[decompiler]] that could [[reverse engineer]] BAC files into their original BASIC-Plus source, complete with original line numbers and variable names (both subsequently worked for DEC). The rest of the memory was used by the BASIC '''RTS''' itself. If one wrote programs in a language that permitted true binary executables such as BASIC-Plus-2, FORTRAN-IV, or Macro Assembler, then the amount of memory available would be 56K (8K allocated to the '''RTS'''). The standard BASIC-PLUS prompt is the "Ready" response, pressing [[Status key|Control-T displays status]] (example):
{{pre|
new
New file name--HWORLD

Ready

{{codett|2=cbmbas|10 Print "Hello World"}}
{{codett|2=cbmbas|20 Input "Press Control-T for 1 line status: ";a$}}
{{codett|2=cbmbas|30 End}}
{{codett|2=cbmbas|run}}
HWORLD  10:17 PM        01-Jan-08
Hello World
Press Control-T for 1 line status: ?
1       KB0     HWORLD+BASIC    KB(0R)  2(16)K+14K      0.2(+0.0) +0

Ready

save

Ready

compile

Ready

{{codett|2=dosbatch|DIR HWORLD.*/na/ex/si/pr}}
SY:[1,2]
HWORLD.BAS       1   < 60>
HWORLD.BAC       7C  <124>

Total of 8 blocks in 2 files in SY:[1,2]

Ready
}}

===DCL (Digital Command Language)===
Starting with Version 9, '''DCL''' became the primary startup '''RTS''' even though it does not have the ability to execute binary programs. This became possible with the advent of the disappearing RSX '''RTS''' (see below). '''DCL''' was incorporated into all of the recent versions of DEC's operating systems (RSX-11, RT-11, [[OpenVMS|VMS]], and later [[OpenVMS]]) for compatibility. The standard '''DCL''' prompt is the dollar "$" sign (example):
<syntaxhighlight lang="console">
$ write 0 "Hello World, it is "+F$TIME()
Hello World, it is 01-Jan-08 10:20 PM
$ inquire p1 "Press Control-T for 1 line status:"
Press Control-T for 1 line status:
1       KB0      DCL+DCL       KB(0R)       4(8)K+24K       0.1(+0.1) -8
$ set verify/debug/watch
$ show memory
(show memory)
(SYSTAT/C)

Memory allocation table:
 Start   End  Length  Permanent   Temporary
   0K -   85K (  86K) MONITOR
  86K - 1737K (1652K)   (User)
1738K - 1747K (  10K)   (User)    DAPRES LIB
1748K - 1751K (   4K)   (User)    RMSRES LIB
1752K - 2043K ( 292K) ** XBUF **
2044K -  *** END ***
$
</syntaxhighlight>

===RSX (Realtime System eXecutive)===
Programs that were written for the RSX '''RTS''' such as COBOL, Macro Assembler, or later releases of BASIC-Plus-2, could use the maximum amount of memory available for a binary program (56K due to the requirements of an '''RTS''' needing the top 8K to use for itself). RSTS Version 7 and later allowed the RSX '''RTS''' to be included in the kernel, making it completely "disappear" from the user address space, thus allowing 64K bytes of memory for user programs.

Programs got around the limitations of the amount of available memory by using libraries (when permissible), by complicated overlay strategies, or by calling other programs ("Chaining") and passing them commands and data in a shared memory area called "Core Common," among other practices. 

When RSX is the default '''KBM''', the standard RSX prompt (both logged in and logged out) is the ">" (or MCR "Monitor Console Routine") sign (example):
<syntaxhighlight lang="doscon">
>run
Please type HELLO
>HELLO 1,1;SECRET
>run
?What?
>help
Valid keyboard commands are:

ASSIGN    DISMOUNT  HELP      RUN     UNSAVE
BYE       EXIT      MOUNT     SHUTUP
DEASSIGN  HELLO     REASSIGN  SWITCH

>run CSPCOM
CSP>HWORLD=HWORLD
CSP>^Z
>RUN TKB
TKB>HWORLD=HWORLD,LB:CSPCOM.OLB/LB
TKB>//
>run HWORLD.TSK
Hello World
Press Control-T for 1 line status: ?
1       KB0     HWORLD+...RSX   KB(0R)  7(32)K+0K       0.8(+0.2) +0

>DIR HWORLD.*/na/ex/si/pr
SY:[1,2]
HWORLD.BAS       1   < 60>
HWORLD.BAC       7C  <124>
HWORLD.OBJ       2   < 60>
HWORLD.TSK      25C  <124>

Total of 35 blocks in 4 files in SY:[1,2]

>
</syntaxhighlight>

===RT-11===
The RT-11 '''RTS''' emulated the Single Job version of the RT-11 distribution. Like the RSX emulation, RT-11 occupied the top 8K of memory, leaving the bottom 56K for '''CUSPS''', programs written in FORTRAN-IV or Macro Assembler. When RT-11 is the default '''KBM''', the standard RT-11 prompt (both logged in and logged out) is the "." sign (example):

<syntaxhighlight lang="man">
.VERSION
Please type HELLO

.HELLO 1,1;SECRET

.VERSION
RT-11SJ V3-03; RSTS/E V8.0

.R PIP
*HWORLD.MAC=KB:
        .MCALL .TTYIN,.PRINT,.EXIT
HWORLD: .ASCII /Hello World/<15><12>
        .ASCIZ /Press Control-T for 1 line status:/
        .EVEN

Start:  .PRINT #HWORLD
        .TTYIN
        .EXIT
        .END    START
^Z
*^Z

.R MACRO
HWORLD=HWORLD
*^Z

.R LINK
*HWORLD=HWORLD
*^Z

.R HWORLD.SAV
Hello World
Press Control-T for 1 line status:
1       KB0     HWORLD+RT11     KB(0R)  2(28)K+4K       0.6(+0.2) +0

..DIR HWORLD.*/na/ex/si/pr
SY:[1,2]
HWORLD.BAS       1   < 60>
HWORLD.BAC       7C  <124>
HWORLD.TSK      25C  <124>
HWORLD.MAC       1   < 60>
HWORLD.OBJ       1   < 60>
HWORLD.SAV       2C  <124>

Total of 37 blocks in 6 files in SY:[1,2]

.
</syntaxhighlight>

===TECO (Text Editor and COrrector)===
The [[TECO (text editor)|TECO editor]] was itself implemented as an RTS to maximize the amount of memory available for the editing buffer, and also because it was first implemented in RSTS V5B, before the release of the general purpose runtime systems (RSX and RT11). TECO was the only RTS distributed with RSTS that did not contain a built-in KBM. The user would start up TECO (like any other program) by running a TECO program (TECO.TEC). TECO and the affine QEDIT were the direct ancestors of the first UNIX-based text editor, ED. Most RSTS systems used CCL's to create a file (MAKE filespec), edit a file (TECO filespec), or run a TECO program (MUNG filespec, data). The following program is an example of how TECO could be used to calculate [[pi]] (currently set to 20 digits):<ref name="StanleyRabinowitz">Greenspon, M.: "The RSTS Crystal Ball – Part 3", p. 12. ''The RSTS Professional Magazine'', October 1, 1982, Vol 4, No 5</ref>
<!-- The ''RSTS Pro'' article contains a few errors, and Micheal does not remember who the original author is, however "bbump" has corrected the errors and attributes Stanley Rabinowitz as the most likely author of this code. -->

<syntaxhighlight lang="text">
Ready

run TECO
*GZ0J\UNQN"E 20UN '
BUH BUV HK
QN< J BUQ QN*10/3UI
QI< \ +2*10+(QQ*QI)UA
B L K QI*2-1UJ QA/QJUQ
QA-(QQ*QJ)-2\ 10@I// -1%I >
QQ/10UT QH+QT+48UW QW-58"E 48UW %V ' QV"N QV^T '
QWUV QQ-(QT*10)UH >
QV^T @^A/
/HKEX$$
31415926535897932384

Ready
</syntaxhighlight>

==RSTS easter eggs==

===System start-up (INIT.SYS)===
If a user typed an unrecognized command at system boot to the "Option:" prompt of INIT.SYS, the startup utility, the message "Type 'HELP' for help" was displayed. If the user subsequently typed 'HELP' (including the quotes) to the prompt, the response was "How amusing, anyway..." followed by the actual help message.

===PDP-11 console lights===
A system manager could compile into the kernel a rotating display pattern that gave the illusion of two snakes chasing each other around the console lights. The normal kernel would give the illusion of one snake moving from right to left in the data lights across the bottom. If the system manager also compiled the "lights" object module the user would see an additional snake moving from left to right in the address lights across the top. This was accomplished by using supervisory mode in the versions prior to 9.0. RSX also had a similar display pattern that would appear as if two snakes were playing chicken and would run into each other in the center of the console.

===Teco easter egg===
The command 'make' allowed a user to make a text file and automatically enter the TECO text editor. If a user typed 'make love', the system created a file called 'love' and typed back, 'Not War?'

===Open Files List===
Kevin Herbert, later working for DEC, added an undocumented feature in the 90's to allow a user to enter {{kbd|^F}} to see a list of open files the user process had, complete with blocks in use and file sizes.

===Stardate===
Beginning with version 9.0, an [[undocumented feature]] would allow the system manager to change the display of the system date. RSTS became the first operating system that would display the system date as a set of numbers representing a [[stardate]] as commonly known from the TV series [[Star Trek: The Original Series|''Star Trek'']].

==Add-ons by other companies==
''[[System Industries]]'' bought the only source license for RSTS to implement an enhancement called {{visible anchor|SIMACS}} (SImultaneous Machine ACceSs), which allowed their special disk controller to set a semaphore flag for disk access, allowing multiple WRITES to the same files on a RSTS System where the disk is shared by multiple PDP-11 RSTS systems. This feature was implemented in System Industries controllers that were attached to many DEC computers and designed by Dr. Albert Chu while he worked at System Industries.

The main innovation was use of a [[semaphore (programming)|semaphore]], a flag to indicate which processor, by cooperative sharing, has exclusive write access.<ref name="SIMACS.HC84">{{cite magazine |last1=Joshi |first1=Prem |last2=Delacroix |first2=Jacques |date=September 1984 |title=New Flexibility For Multiple VAX/VMS |magazine=[[HARDCOPY]] |pages=64–68}}</ref>

This required many changes to the way access to disks was accomplished by the RSTS operating system. The FIPS (File Information Processing System) system, that handled i/o access, was single-threaded in RSTS. To allow a disk access to stall while another machine had active access to a block, required that the FIPS could timeout a request, go to the next request and 'come back' to the stalled one in a [[Round-robin scheduling|round robin]] fashion. The code to allow this was written by Philip Hunt while working at System Industries, in [[Milpitas, California]]. He eventually worked for Digital Equipment in the New England area in the late 1980s and early 1990s.

''SIMACS''<ref>{{cite web
   |url=http://archive.computerhistory.org/resources/access/text/2017/06/102726714-05-05-acc.pdf
   |title=Burton Grad Associates
   |quote=SIMACS (System Industries Multiple Access Control System)
   |date=March 27, 1986}}</ref> was not limited to the ''PDP-11'' product line; ''VAXen'' could also use it.<ref name=SIMACS.HC84/>

==RSTS emulations==

===ROSS/V===
In 1981, Evans Griffiths & Hart marketed the ''ROSS/V'' product. ''ROSS/V'' allowed all user mode processes of RSTS ('''CUSPS''', '''RTS'''s and user programs) the ability to run unmodified under VMS on the VAX-11 machines. The code for this emulation handled all of the kernel processes that would normally be handled by a RSTS kernel running on a PDP-11. The original BASIC-PLUS language that has carried through all versions of RSTS was subcontracted by Evans Griffiths & Hart, Inc. for a fixed price of $10,500.<ref name="PeterDickRSTS80th">{{cite web|url=http://www.silverware.co.uk/rsts_80th_birthday.htm|title=RSTS 80th Birthday|work=silverware.co.uk|access-date=December 26, 2016}}</ref>

===Other PDP-11 emulators===
RSTS and its applications can run under a number of PDP-11 emulators such as [[SIMH]] and [[PDP-11#Ersatz-11|Ersatz-11]]. For more information, see [[PDP-11#Emulators|PDP-11]].

==RSTS mascot==

===Spike and Albert===

==Versions==
RSTS was originally called ''BTSS'' (Basic Time Sharing System). Before shipment began, the name was changed from BTSS to RTSS because a product called BTSS was already being marketed by [[Honeywell]]. A simple typing mistake changed the name from RTSS to RSTS.<ref name="PeterDickRSTS80th"/>

{| class="wikitable" style="font-size: smaller;"
! Version !! Release date !! Notes
|-
| 1 || Never released ||
|-
| 2A-19 || 1971 || Installed at [[Carleton College]] and [[Seattle Pacific College]].
|-
| 2B || June 1971 || Installed at the Delaware School Auxiliary Association.<ref>{{Cite web|url=http://www.project-delta.net/teresa.html|title = Teresa Green's memoir of DELTA}}</ref>
|-
| 2C || October 1971 || Enhanced software support (record I/O)
|-
| 3A-19 || January 1972 ||
|-
| 3B || May 1972 ||
|-
| 3C || June 1972 || Enhanced software support (UPDATE mode)
|-
| 4A-12 || October 1972 || New hardware supported.
|-
| 4B || July 1975 || A patched version of V4A with no new features
|}

The addition of new memory management support and the ability to install more memory in the PDP-11/40 and PDP-11/45 led to another name change: RSTS-11 now became RSTS/E.

{| class="wikitable" style="font-size: smaller;"
! Version !! Release date !! Notes
|-
| 5A-21 || July 1973 || Memory management extensions from 64KB to 256KB.
|-
| 5B-24 || November 1974 || Multiple SWAP files, RTS and CCL introduced.
|-
| 5C-01 || March 1975 || A patched version of V5B with no new features.
|-
| 6A-02 || August 1975 || New hardware, 22 bit addressing (2 MB), 63 jobs.
|-
| 6B-02 || February 1977 || New hardware, SYSGEN under RT-11, CCL at runtime.
|-
| 6C-03 || February 1978 || DECnet Phase II, DTR, DIBOL supported. SUPERVISOR mode.
|-
| 7.0 || August 1978 || New hardware, (4 MB), RDC support.
|-
| 7.1 || February 1981 || [[Kernel mode]] Instruction & Data space support, DECnet Phase III.
|-
| 7.2 || August 1982 || New hardware (UDA50 drives).
|-
| 8.0-06 || April 1983 || New hardware (MicroPDP-11).
|-
| 9.0-14 || May 1985 || New hardware, DCL default, PBS, multiple privs, [[key derivation function|hashed passwords]], new Backup utility, and Stardate.
|-
| 9.1-05 || October 1985 || Enhanced hardware support, multi-threaded FIP, LOAD INDEX.
|-
| 9.2-10 || June 1986 || New hardware supported.
|-
| 9.3-20 || January 1987 || Enhanced hardware support, DECnet Phase IV.
|-
| 9.4 || July 1987 || New hardware, Scheduler and Terminal Service improvements.
|-
| 9.5-08 || December 1987 || Clustersize increased to 64, BACKUP/DIR added.
|-
| 9.6 || September 1988 || LAT support, HELP SPIKE.
|-
| 9.7 || July 1989 || New hardware, DV0: at runtime, ANSI PDP-11C available.
|-
| 10.0 || May 1990 || Command line history in TTDRV.
|-
| 10.1 || September 1992 || Y2K fixes.
|}

===Clones in the USSR===
*[[DOS-KP]] ("ДОС-КП")

==Applications==
Computer [[service bureau|bureau]]s sometimes deployed User-11 for RSTS/E-based [[data management]].<ref>
{{cite journal
| date= 1983-07-18
| title= Productivity Aid Replaces Bureau's Cobol Code
| journal= Computerworld
| pages= 40
| access-date= 2011-12-26
| url= https://books.google.com/books?id=OL640VLAZo4C
| quote= User-11 [...] a data management system for (DEC) PDP-11s running under the RSTS/E operating system [...]
}}
</ref>

==See also==
*[[Asynchronous System Trap]]
*[[BASIC-PLUS#BASIC Plus 2|BASIC-Plus-2]]
*[[OS/8#The Concise Command Language|Concise Command Language]]
*[[DATATRIEVE]]
*[[DECnet]]
*[[Front panel]]
*[[Kevin Mitnick]]
*[[Local Area Transport]]
*[[Octal Debugging Technique]]
*[[QIO]]
*[[Record Management Services]]
*[[Runtime system]]
*[[Time-sharing]]
*[[Time-sharing system evolution]]

==References==
{{Reflist}}

==External links==
*[http://elvira.stacken.kth.se Elvira at The Royal Institute of Technology in Stockholm, Sweden]
*[http://www.rsts.org RSTS Hobbyist Site]
*[http://simh.trailing-edge.com SimH web page]
*[http://www.woffordwitch.com Wofford Witch]

{{Digital Equipment Corporation}}
{{Time-sharing operating systems}}

{{DEFAULTSORT:Rsts E}}
[[Category:DEC operating systems]]
[[Category:PDP-11]]
[[Category:Discontinued operating systems]]
[[Category:Time-sharing operating systems]]
[[Category:Assembly language software]]
[[Category:1970 software]]