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TOPS-20

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TOPS-20
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DeveloperDigital Equipment Corporation
Written inAssembly language
OS familyTENEX
Working stateDiscontinued
Initial release1976; 48 years ago (1976)
Latest release7.1 / June 1988; 36 years ago (1988-06)
Marketing targetMainframe computers
Available inEnglish
PlatformsPDP-10
Default
user interface		Command-line interface
LicenseProprietary
Preceded byTENEX

The TOPS-20 operating system by Digital Equipment Corporation (DEC) is a proprietary[1] OS used on some of DEC's 36-bit mainframe computers. The Hardware Reference Manual was described as for "DECsystem-10/DECSYSTEM-20 Processor" (meaning the DEC PDP-10 and the DECSYSTEM-20).[2]

TOPS-20 began in 1969 as the TENEX operating system of Bolt, Beranek and Newman (BBN) and shipped as a product by DEC starting in 1976.[3] 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, ITS[4] and WAITS—all of which were notable time-sharing systems for the PDP-10 during this timeframe.

TENEX

Main article: 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.

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,[5] 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.[6]

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."[6]

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[2]
  • JSYS (Jump to System) calls from MACro-language (.MAC) programs[7][8]

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:

  • noise-words - typing DIR and then pressing the ESCape key resulted in
DIRectory (of files)
typing I and pressing the Esc key resulted in
Information (about)

One could then type ? to find out what operands were permitted/required. Pressing Ctrl-T displays status information.

Commands

The following list of commands are supported by the TOPS-20 Command Processor.[2]

  • 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
  • R
  • 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

JSYS features

JSYS stands for Jump to SYStem.[9] 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."[2]

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.[10][11][12][13]

PCL language features

PCL includes:[10]

  • 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

References

  1. ^ Richard Stallman (30 October 1986). "RMS lecture at KTH (Sweden)".
  2. ^ a b c d "TOPS-20 Command manual" (PDF).
  3. ^ a b "Origins and Development of TOPS-20".
  4. ^ "ITS reference manual" (PDF).
  5. ^ "What does UUO mean in Software?". abbreviations.com.
  6. ^ a b The 10/50 was the top-of-the-line KA machine at that time. Dan Murphy (1989). "Origins and Development of TOPS-20". The family continued with another KA, the 10/55, and then came KI, KL & KS.
  7. ^ 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
  8. ^ "DECSYSTEM-20 Assembly Language Guide". The Kermit Project. 3 July 1980.
  9. ^ "JSYS means Jump to System". allacronyms.com.
  10. ^ a b TOPS-20 Programmable Command Language / User's Guide and Reference Manual. Carnegie Mellon University Computation Center. 1981.
  11. ^ "Programmable Command Language". March 11, 2016.
  12. ^ R. J. Cohn (1988). "Programmable Command Languages for Window System" (PDF).
  13. ^ "TOPS-20 Programmable Command Language".

Further reading

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