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DeveloperDigital Equipment Corporation
Written inALGOL, BASIC, FOCAL, Fortran D, PAL-D
Working stateDiscontinued
Source modelClosed source
Initial release1968; 56 years ago (1968)
Latest release8.24 / January 1975; 49 years ago (1975-01)[1][2]
PlatformsPDP-8 starting with the PDP-8I model
Kernel typeTime-sharing operating systems
Influenced byTSS/360
user interface
Command-line interface
Succeeded byPS/8 and OS/8

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 later the EduSystem 50.[3]: p.2-15 

The operating system runs on the 12-bit PDP-8 computer starting with the PDP-8I model 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 is 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 (8K for the operating system and 4K for the user swap area) and a swapping device; The standard swapping device, called a drum, was a disk drive with a head assigned to each track so there was no delay waiting for a read/write head to be repositioned on the drive. On a 24K word machine, it can give good support for its maximum of 16 users.[1]

Each user gets a virtual 4K PDP-8; many of the utilities users run on these virtual machines are 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 is well supported, while restricted (4K) versions of FORTRAN D and Algol are available.[6]

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

  • FORTRAN-D can only access 2 data files at a time, and the entire program is MAIN: no subroutines.
  • BASIC-8 programs are limited to 350 lines, but "chaining" allows "programs of virtually any length." BASIC-8 is based on Dartmouth BASIC but lacks matrix operations, implicit declaration of small arrays, strings, ON-GOTO/GOSUB, TAB, and multiline DEF FN statements.[7]
  • PAL-D (Program Assembly Language/Disk) allows the "full standard" but, like all TSS/8 programs, is restricted to 4K. Many programs designed to work on a stand-alone machine and manipulate hardware directly would still work on TSS-8 as it emulated many I/O requests internally.
  • ALGOL[8] is implemented as a known standard subset, "IFIP Subset ALGOL 60."

It also supports DEC's FOCAL-8, which has been available from earlier PDP/8 models and it provides an algebraic language as well as a desk calculator mode.


TSS/8 sold more than 100 copies.[3]: 2–16 

Operating costs were about 1/20 of TSS/360. TSS/8 is 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 (1978). 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. S2CID 16325116.