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DeveloperDigital Equipment Corporation
Written inALGOL, BASIC, FOCAL, Fortran D, PAL-D
Working stateDiscontinued
Source modelClosed source
Initial release1968; 54 years ago (1968)
Latest release8.24 / January 1975; 47 years ago (1975-01)[1][2]
Kernel typeTime-sharing operating systems
Influenced byTSS/360
user interface
Command-line interface
Succeeded byRSTS-11

TSS/8 is a discontinued time-sharing operating system co-written by Don Witcraft and John Everett at Digital Equipment Corporation in 1967. DEC also referred to it as Timeshared-8 and EduSystem 50.[3]: p.2-15 

The operating system ran on the 12-bit PDP-8 computer and was released in 1968.


TSS/8 was designed at Carnegie Mellon University with graduate student Adrian van de Goor, in reaction to the cost, performance, reliability, and complexity of IBM's TSS/360 (for their Model 67).[4]: 180 

Don Witcraft wrote the TSS/8 scheduler, command decoder and UUO (Unimplemented User Operations) handler. John Everett wrote the disk handler, file system, TTY (teletypewriter) handler and 680-I service routine for TSS/8. Roger Pyle and John Everett wrote the PDP-8 Disk Monitor System, and John Everett adapted PAL-III to make PAL-D for DMS. Bob Bowering, author of MACRO for the PDP-6 and PDP-10, wrote an expanded version, PAL-X, for TSS/8.[5]


This timesharing system:

was based on a protection architecture proposed by Adrian Van Der Goor, a grad student of Gordon Bell's at Carnegie-Mellon. It requires a minimum of 12K words of memory and a swapping device; on a 24K word machine, it could give good support for 17 users.[1] Each user gets a virtual 4K PDP-8; many of the utilities users ran on these virtual machines were only slightly modified versions of utilities from the Disk Monitor System or paper-tape environments. Internally, TSS/8 consists of RMON, the resident monitor, DMON, the disk monitor (file system), and KMON, the keyboard monitor (command shell). BASIC was well supported, while restricted (4K) versions of FORTRAN D and Algol were available.[6]

Like IBM's CALL/OS, it implemented language variants:[3]: pp.2-16 thru 2-18 

  • FORTRAN-D could only access 2 data files at a time, and the entire program was MAIN: no subroutines.
  • BASIC-8 programs were limited to 350 lines, but "chaining" allowed "programs of virtually any length." BASIC-8 was based on Dartmouth BASIC but lacked matrix operations, implicit declaration of small arrays, strings, ON-GOTO/GOSUB, TAB, and multiline DEF FN statements.[7]
  • PAL-D (Program Assembly Language/Disk) allowed the "full standard" but, like all TSS/8 programs, was restricted to 4K.
  • ALGOL[8] was implemented as a known standard subset, "IFIP Subset ALGOL 60."

It also supported DEC's FOCAL, which was "developed specifically for the PDP 8/E" and it provided "an algebraic language" and also a "desk calculator mode."

Historical notes[edit]

  • TSS/8 sold more than 100 copies.[3]: 2–16 
  • Operating costs were about 1/20 of TSS/360. TSS/8 was also designed to be more cost-effective than the PDP-10 "for jobs with low computational requirements (like editing)".[9]
  • The RSTS-11 operating system is a descendant of TSS/8.[4]: 181 


  1. ^ a b Remy van Elst (July 26, 2015). "Running TSS/8 on the DEC PiDP-8/i and SIMH". Raymii.org.
  2. ^ "PDP-8 Digital Software News" (PDF). March 1976. DEC-08-XSMAD-A-D. {{cite magazine}}: Cite magazine requires |magazine= (help)
  3. ^ a b c PDP-8/E PDP-8/M & PDP-8/F Small Computer Handbook (PDF). Digital Equipment Corporation. 1973.
  4. ^ a b C. Gordon Bell; J. Craig Mudge; John N. McNamara. Computer Engineering: A DEC View of Hardware Systems Design (PDF). Digital Press. ISBN 0-932376-00-2.
  5. ^ "Who's Who?". PDP-8 Frequently Asked Questions.
  6. ^ "What operating systems were written for the PDP-8?". PDP-8 Frequently Asked Questions.
  7. ^ "Appendix E: Implementation Notes, page E-1" (PDF).
  8. ^ "TSS/8 ALGOL".
  9. ^ Ad van de Goor; C. Gordon Bell; Donald A. Witcraft (November 1969). "Design and Behavior of TSS/8: a PDP-8 Based Time-sharing System" (PDF). IEEE Transactions on Computers. 18 (11): 1038–1043. doi:10.1109/T-C.1969.222577.