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

DeveloperDigital Equipment Corporation
Written inALGOL, BASIC, FOCAL, Fortran D, PAL-D
OS familyDEC OS family
Working stateDiscontinued
Source modelClosed source
Initial release1968; 52 years ago (1968)
Latest release8.24 / January 1975; 45 years ago (1975-01)[1][2]
Kernel typeTime-sharing operating systems
Default user interfaceCommand-line interface

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]

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.[6]

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.[7]

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 programs were limited to 350 lines, but "chaining" allowed "programs of virtually any length."
  • PAL-D (Program Assembly Language/Disk) allowed the "full standard" but, like all TSS-8 programs, was restricted to 4K.
  • ALGOL 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 notesEdit

  • TSS/8 sold more than 100 copies[8][3]
  • Operating costs were about 1/20th 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][10]
  • The RSTS-11 operating system is a descendant of TSS-8.[11]


  1. ^ "Running TSS/8 on the DEC PiDP-8/i and SIMH - Raymii.org".
  2. ^ "Digitol Software News" (PDF).
  3. ^ a b c in PDP 8/e Small Computer Handbook. Digital Equipment Corporation. 1973.
  4. ^ p.180,COMPUTER ENGINEERING" (C)'78 by DEC/Digital Press. C.Gordon Bell, J.Craig Mudge, John N. McNamara, ISBN 0-932376-00-2
  5. ^ FAQs
  6. ^ https://raymii.org/s/articles/Running_TSS_8_on_the_DEC_PiDP-8_i_and_SIMH.html
  7. ^ FAQs
  8. ^ "More than 100 ... in use today.." {1973)
  9. ^ http://www.computer.org/csdl/trans/tc/1969/11/01671170-abs.html
  10. ^ http://research.microsoft.com/en-us/um/people/gbell/CGB%2520Files/Design%2520and%2520Behavior%2520of%2520TSS8%2520IEEE%25206906%2520c.pdf
  11. ^ p.181,COMPUTER ENGINEERING" (C)'78 by DEC/Digital Press. C.Gordon Bell, J.Craig Mudge, John N. McNamara, ISBN 0-932376-00-2