TOPS-20

{{Main|TENEX (operating system)}}

TOPS-20 was based upon the TENEX operating system, which had been created by 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.

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,{{cite web |url=http://www.abbreviations.com/term/223192 |title=What does UUO mean in Software?

|website=abbreviations.com}} 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.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.

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."

The major ways to get at TOPS-20 capabilities, and what made TOPS-20 important, were

• Commands entered via the command processor, EXEC.EXE
• JSYS (Jump to System) calls from MACro-language (.MAC) programsThe 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{{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}}

The "EXEC" accomplished its work primarily using

• internal code, including calls via JSYS
• requesting services from "GALAXY" components (e.g. spoolers)

Rather advanced for its day were some TOPS-20-specific features:

• Command completion
• 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 information.

The following list of commands are supported by the TOPS-20 Command Processor.

{{div col|colwidth=9em}}

• ACCESS
• ADVISE
• APPEND
• ARCHIVE
• ASSIGN
• ATTACH
• BACKSPACE
• BLANK
• BREAK
• BUILD
• CANCEL
• CLOSE
• COMPILE
• CONNECT
• CONTINUE
• COPY
• CREATE
• CREF
• CSAVE
• DAYTIME
• DDT
• DEASSIGN
• DEBUG
• DEFINE
• DELETE
• DEPOSIT
• DETACH
• DIRECTORY
• DISABLE
• DISCARD
• DISMOUNT
• EDIT
• ENABLE
• END-ACCESS
• EOF
• ERUN
• EXAMINE
• EXECUTE
• EXPUNGE
• FDIRECTORY
• FORK
• FREEZE
• GET
• HELP
• INFORMATION
• KEEP
• LOAD
• LOGIN
• LOGOUT
• MERGE
• MODIFY
• MOUNT
• PERUSE
• PLOT
• POP
• PRINT
• PUNCH
• PUSH
• RECEIVE
• REENTER
• REFUSE
• REMARK
• RENAME
• RESET
• RETRIEVE
• REWIND
• RUN
• SAVE
• SEND
• SET
• SET HOST
• SKIP
• START
• SUBMIT
• SYSTAT
• TAKE
• TALK
• TDIRECTORY
• TERMINAL
• TRANSLATE
• TYPE
• UNATTACH
• UNDELETE
• UNKEEP
• UNLOAD
• VDIRECTORY

{{div col end}}

JSYS stands for Jump to SYStem.{{cite news |url=https://www.allacronyms.com/JSYS/Jump_to_System |title=JSYS means Jump to System |newspaper=All Acronyms}} 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."

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) 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.{{cite book

|title=TOPS-20 Programmable Command Language / User's Guide and Reference Manual

|publisher=Carnegie Mellon University Computation Center |year=1981}}{{cite web

|url=http://fileformats.archiveteam.org/wiki/Programmable_Command_Language

|title=Programmable Command Language

|website=fileformats.archiveteam.org

|date=March 11, 2016}}{{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}}{{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}}

PCL includes:

• 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)

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.

• Time-sharing system evolution

{{Reflist}}

• [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]."

• [http://www.vt100.net/timeline/1976.html DIGITAL Computing Timeline]
• [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] 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