View source for TOPS-20

{{Short description|Operating system by Digital Equipment Corporation}}
{{Infobox OS
| name = TOPS-20
| logo =
| screenshot = TOPS-20.png
| caption = login
| developer = [[Digital Equipment Corporation]]
| source_model = 
| kernel_type = 
| supported_platforms = [[PDP-10]]
| released = {{Start date and age|1976}}
| latest_release_version = 7.1
| latest_release_date = {{Start date and age|1988|06}}
| marketing_target = [[Mainframe computer]]s
| programmed_in = [[Assembly language]]
| language = [[English language|English]]
| updatemodel = 
| package_manager = 
| working_state = Discontinued
| ui = [[Command-line interface]]
| license = [[Proprietary software|Proprietary]]
| preceded by = [[TENEX (operating system)|TENEX]]
| succeeded by =
| website =
| family = [[TENEX (operating system)|TENEX]]
}}
The '''TOPS-20''' [[operating system]] by [[Digital Equipment Corporation]] (DEC) is a proprietary<ref>{{cite web|url=https://www.gnu.org/philosophy/stallman-kth.html|title=RMS lecture at KTH (Sweden)|date=30 October 1986|author=Richard Stallman}}</ref> OS used on some of DEC's 36-bit [[mainframe computer]]s. The Hardware Reference Manual was described as for "DECsystem-10/DECSYSTEM-20 Processor" (meaning the DEC [[PDP-10]] and the [[DECSYSTEM-20]]).<ref name=CMDref>{{cite web
|url=https://livingcomputers.org/UI/UserDocs/TOPS-20-v7-1/2_TOPS-20_Commands_Reference_Manual.pdf
|title=TOPS-20 Command manual
|date=September 1985
|publisher=Digital Equipement Corporation
|access-date=2024-02-10
|archive-date=2024-06-16
|archive-url=https://web.archive.org/web/20240616125757/https://livingcomputers.org/UI/UserDocs/TOPS-20-v7-1/2_TOPS-20_Commands_Reference_Manual.pdf
|url-status=dead
}}</ref>

TOPS-20 began in 1969 as the [[TENEX (operating system)|TENEX]] operating system of [[Bolt, Beranek and Newman]] (BBN) and shipped as a product by DEC starting in 1976.<ref name=TENXref>{{cite web|url=http://tenex.opost.com/hbook.html|title=Origins and Development of TOPS-20}}</ref>  TOPS-20 is almost entirely unrelated to the similarly named [[TOPS-10]], but it was shipped with the PA1050 TOPS-10 Monitor Calls emulation facility which allowed most, but not all, TOPS-10 executables to run unchanged. As a matter of policy, DEC did not update PA1050 to support later TOPS-10 additions except where required by DEC software.

TOPS-20 competed with TOPS-10,  [[Incompatible Timesharing System|ITS]]<ref>{{cite web
|url=https://dspace.mit.edu/bitstream/handle/1721.1/6165/AIM-161A.pdf
|title=ITS reference manual
}}</ref> and [[WAITS]]—all of which were [[Time-sharing#Notable time-sharing systems|notable time-sharing systems]] for the [[PDP-10]] during this timeframe. TOPS-20 is informally known as TWENEX.<ref>{{cite web|url=http://www.catb.org/jargon/html/T/TWENEX.html|title=TWENEX|website=The Jargon File}}</ref>

==TENEX==
{{Main|TENEX (operating system)}}
TOPS-20 was based upon the [[TENEX (operating system)|TENEX]] operating system, which had been created by [[BBN Technologies|Bolt Beranek and Newman]] for Digital's [[PDP-10]] computer. After Digital started development of the KI-10 version of the PDP-10, an issue arose: by this point TENEX was the most popular customer-written PDP-10 operating systems, but it would not run on the new, faster KI-10s. To correct this problem, the DEC PDP-10 sales manager purchased the rights to TENEX from BBN and set up a project to port it to the new machine. In the end, very little of the original TENEX code remained, and Digital ultimately named the resulting operating system TOPS-20.

==PA1050==
Some of what came with TOPS-20 was merely an emulation of the [[TOPS-10]] Operating System's calls. These were known as UUO's, standing for Unimplemented User Operation,<ref>{{cite web |url=http://www.abbreviations.com/term/223192 |title=What does UUO mean in Software?
 |website=abbreviations.com}}</ref> and were needed both for compilers, which were not 20-specific, to run, as well as user-programs written in these languages. The package that was mapped into a user's address space was named PA1050: PA as in PAT as in compatibility; 10 as in DEC or PDP 10; 50 as in a PDP 10 Model 50, 10/50, 1050.<ref name=JSYS104>The 10/50 was the top-of-the-line KA machine at that time. {{cite web |url=http://tenex.opost.com/hbook.html
|title=Origins and Development of TOPS-20 |author=Dan Murphy  |date=1989}} The family continued with another KA, the 10/55, and then came KI, KL & KS.</ref>

Sometimes PA1050 was referred to as PAT, a name that was a good fit to the fact that PA1050, "was simply unprivileged user-mode code" that "performed the requested action, using JSYS calls where necessary."<ref name=JSYS104 />

==TOPS-20 capabilities==
The major ways to get at TOPS-20 capabilities, and what made TOPS-20 important, were
* Commands entered via the command processor, EXEC.EXE<ref name=CMDref />
* JSYS (Jump to System) calls from MACro-language (.MAC) programs<ref>The JSYS was the counterpart for the 20 of what was done by TOPS-10 on a "10" and thus the emulator for a DEC PDP-10 Model 50 was what PA1050 was emulating.  The 10's system calls were known as UUO's</ref><ref>{{cite web| url=http://www.columbia.edu/kermit/ftp/dec20/assembler-guide.txt |title= DECSYSTEM-20 Assembly Language Guide |date=3 July 1980 |website=The Kermit Project}}</ref>

The "EXEC" accomplished its work primarily using
* internal code, including calls via JSYS
* requesting services from "GALAXY" components (e.g. spoolers)

===Command processor===
Rather advanced for its day were some TOPS-20-specific features:
* [[Command-line completion|Command completion]]<ref name=TENXref />
* Dynamic help in the form of 
:*''noise-words'' - typing DIR and then pressing the ESCape key resulted in
::::DIRectory (of files)
::typing {{keypress|I}} and pressing the {{keypress|Esc}} key resulted in
:::: Information (about)

One could then type {{keypress|?}} to find out what operands were permitted/required.  Pressing {{keypress|Ctrl|T}} displays [[Status key|status information]].
===Available programming languages===
Some available programming languages were [[FORTRAN]], [[COBOL]], [[BASIC]], [[ALGOL]], [[CPL_(programming_language)|CPL]], and [[APL_(programming_language)|APL]].<ref>{{Cite web|url=http://www.vt100.net/timeline/1976.html|title=DIGITAL Computing Timeline|website=vt100.net}}</ref>

===Commands===
The following list of [[command (computing)|commands]] are supported by the TOPS-20 Command Processor.<ref name=CMDref />

{{div col|colwidth=9em}}

* ACCESS
* ADVISE
* [[append|APPEND]]
* ARCHIVE
* ASSIGN
* ATTACH
* BACKSPACE
* BLANK
* BREAK
* BUILD
* CANCEL
* CLOSE
* COMPILE
* CONNECT
* CONTINUE
* [[copy (command)|COPY]]
* CREATE
* CREF
* CSAVE
* DAYTIME
* [[Dynamic debugging technique|DDT]]
* DEASSIGN
* [[debug (command)|DEBUG]]
* DEFINE
* [[del (command)|DELETE]]
* DEPOSIT
* DETACH
* [[dir (command)|DIRECTORY]]
* DISABLE
* DISCARD
* DISMOUNT
* EDIT
* ENABLE
* END-ACCESS
* EOF
* ERUN
* EXAMINE
* EXECUTE
* EXPUNGE
* FDIRECTORY
* FORK
* FREEZE
* GET
* [[help (command)|HELP]]
* INFORMATION
* KEEP
* LOAD
* [[Login|LOGIN]]
* LOGOUT
* MERGE
* MODIFY
* [[Mount (computing)|MOUNT]]
* PERUSE
* PLOT
* POP
* [[print (command)|PRINT]]
* PUNCH
* PUSH
* RECEIVE
* REENTER
* REFUSE
* [[Comment (computer programming)|REMARK]]
* [[ren (command)|RENAME]]
* RESET
* RETRIEVE
* REWIND
* [[Run command|RUN]]
* SAVE
* SEND
* SET
* SET HOST
* SKIP
* [[start (command)|START]]
* SUBMIT
* SYSTAT
* TAKE
* TALK
* TDIRECTORY
* TERMINAL
* TRANSLATE
* [[TYPE (DOS command)|TYPE]]
* UNATTACH
* [[Undeletion|UNDELETE]]
* UNKEEP
* UNLOAD
* VDIRECTORY

{{div col end}}

===JSYS features===
JSYS stands for '''J'''ump to '''SYS'''tem.<ref>{{cite news |url=https://www.allacronyms.com/JSYS/Jump_to_System |title=JSYS means Jump to System |newspaper=All Acronyms}}</ref>  Operands were at times memory addresses. "TOPS-20 allows you to use 18-bit or 30-bit  addresses. Some  monitor calls require one kind, some the other;  some calls accept either kind. Some monitor calls use only 18 bits to hold an address. These  calls interpret 18-bit addresses as locations in the current section."<ref name=CMDref />

Internally, files were first identified, using a GTJFN (Get Job File Number) JSYS, and then that JFN number was used to open (OPENF) and manipulate the file's contents.

==PCL (Programmable Command Language)==
'''PCL (Programmable Command Language)''' is a programming language that runs under TOPS-20. PCL source programs are, by default, stored with Filetype .PCL, and enable extending the TOPS-20 EXEC via a verb named DECLARE. Newly compiled commands then become functionally part of the EXEC.<ref name=PCLman>{{cite book
   |title=TOPS-20 Programmable Command Language / User's Guide and Reference Manual
   |publisher=Carnegie Mellon University Computation Center |year=1981}}</ref><ref>{{cite web
|url=http://fileformats.archiveteam.org/wiki/Programmable_Command_Language
|title=Programmable Command Language
|website=fileformats.archiveteam.org 
|date=March 11, 2016}}</ref><ref>{{cite web
   |url=http://reports-archive.adm.cs.cmu.edu/anon/scan/CMU-CS-88-139.pdf
   |title=Programmable Command Languages for Window System
   |author=R. J. Cohn  |year=1988
   |archive-url=https://web.archive.org/web/20030926230320/http://reports-archive.adm.cs.cmu.edu/anon/scan/CMU-CS-88-139.pdf
   |archive-date=2003-09-26}}</ref><ref>{{cite web
|url=http://www.math.utah.edu/~bowman/pcl.txt
|title=TOPS-20 Programmable Command Language
|author=Ray Scott
|date=12 January 1983
|archive-url=https://web.archive.org/web/20081007044359/http://www.math.utah.edu/~bowman/pcl.txt
|archive-date=2008-10-07}}</ref>

===PCL language features===
PCL includes:<ref name=PCLman/>
* flow control: DO While/Until, CASE/SELECT, IF-THEN-ELSE, GOTO
* character string operations (length, substring, concatenation)
* access to system information (date/time, file attributes, device characteristics)

==TOPS-20 today ==
[[Paul Allen]] maintained several publicly accessible historic computer systems before his death, including an [[XKL]] TOAD-2 running TOPS-20.

See also [[SDF Public Access Unix System]].

==See also==
* [[Time-sharing system evolution]]

==References==
{{Reflist}}

==Further reading==
* ''[http://tenex.opost.com/fjcc72/ Storage Organization and Management in TENEX]''.  Daniel L. Murphy.  AFIPS Proceedings, 1972 FJCC.
* ''Implementation of TENEX on the KI10''.  Daniel L. Murphy.  TENEX Panel Session, NCC 1974.
* "[http://tilt.twenex.org TOPS-20 User's Guide] {{Webarchive|url=https://web.archive.org/web/20140107050623/http://tilt.twenex.org/ |date=2014-01-07 }}." 1988.
* "[http://www.columbia.edu/kermit/ftp/dec20/assembler-guide.txt DECSYSTEM-20 Assembly Language Guide]." Frank da Cruz and Chris Ryland, 1980.
* "[http://gunkies.org/wiki/Running_TOPS-20_V4.1_under_SIMH Running TOPS-20 V4.1 under the SIMH Emulator]."

==External links==
* [http://tenex.opost.com/hbook.html Origins and Development of TOPS-20] is an excellent longer history.
* [http://panda.trailing-edge.com Panda TOPS-20 distribution].
* [http://www.twenex.org SDF Public Access TWENEX].
* [http://simh.trailing-edge.com SIMH Simulator] capable of simulating the PDP-10 and running TOPS-20.
* [http://www.36bit.org/dec/manual/ Manuals for DEC 36-bit computers] {{Webarchive|url=https://web.archive.org/web/20140302093233/http://www.36bit.org/dec/manual/ |date=2014-03-02 }}.
* [http://pdp-10.trailing-edge.com PDP-10 Software Archive].
* [http://www.inwap.com/pdp10/ 36-bits Forever].
* [https://livingcomputers.org/Computer-Collection/Online-Systems/Request-A-Login.aspx Request a login] {{Webarchive|url=https://web.archive.org/web/20200528215220/https://www.livingcomputers.org/Computer-Collection/Online-Systems/Request-A-Login.aspx |date=2020-05-28 }} to [[Living Computers: Museum + Labs]] TOAD-2 running TOPS-20.

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

[[Category:DEC operating systems]]
[[Category:Time-sharing operating systems]]
[[Category:1969 software]]