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The TOPS-10 System was a computer operating system from Digital Equipment Corporation (DEC) for the PDP-10 released in 1964, the resulting systems being referred to as "DECsystem-10. TOPS means Timesharing / Total OPerating System.


TOPS-10 supported shared memory and allowed the development of one of the first true multiplayer computer games. The game was called DECWAR and was a text-oriented Star Trek type game. Users at terminals typed in commands and fought each other in real time.

Another groundbreaking application was called FORUM. This application was perhaps the first so-called CB Simulator that allowed users to converse with one another in what is now known as a chat room. This application showed the potential of multiuser communication and led to the development of CompuServe's chat application.

TOPS-10 had a very robust API that used a mechanism called a UUO which is an acronym for Unimplemented User Operation. UUOs implemented operating system calls in a way that made them look like machine instructions. The API was called Monitor Calls and was very much ahead of its time like most of the operating system. System programming on DECsystem-10s was simple and powerful thanks to this extremely flexible operating system API.

TOPS-10 had an interesting scheduler with many run queues, unlike OpenVMS for example which has two run queues, and inserts processes into the queue depending on process priority. The TOPS-10 Operating System also included User file and Device independence.

TOPS-10 was a very fast and flexible operating system that was far ahead of its time.

Release history

The final release of TOPS-10 was version 7.04.

Latter day implementations

Hobbyists are now entitled to set up and use TOPS-10 under a Hobbyist's License.

The easiest way for the hobbyist to run TOPS-10 is to acquire a suitable emulator and an operating system image. TOPS-10 may also be generated from archived original distribution "tapes".

Paul Allen maintains several publicly accessible historic computer systems, including a DECsystem-1090 running TOPS-10.

Implemented programming languages

The TOPS-10 assembler, MACRO-10, was bundled with the TOPS-10 distribution.

The following programming languages were implemented on TOPS-10 as layered products:

  • ALGOL, as ALGOL-10 v10B, a compiler used for general computing
  • APL, as APL-SF V2, an interpreter used for mathematical modelling
  • BASIC, as BASIC-10 v17F, an interpreter used for general computing
  • BLISS, as BLISS-36, a compiler used for systems programming
  • COBOL, as COBOL-68 and COBOL-74, compilers used for business computing
  • Fortran, as FORTRAN-10 v11, a compiler used for numerical computing

The following programming languages were implemented on TOPS-10 as contributions from DECUS members:

  • FOCAL, as FOCAL-10
  • Forth, a threaded interpreted language
  • IMP72
  • Lisp, an interpreter used for AI programming
  • Pascal, a compiler used for computing education
  • SAM76
  • Simula, a compiler used for modeling
  • SNOBOL, an interpreter used for string processing

Implemented user utilities

The following major user utilities were implemented on TOPS-10:

  • RMS (Records Management Services)
  • IQL (Interactive Query language)

Notable games implemented on TOPS-10


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