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Developer Digital Equipment Corporation
Written in ALGOL, BASIC, FOCAL, Fortran D, PAL-D
OS family DEC OS family
Working state Discontinued
Source model Closed source
Latest release 8.24 / February 1975 [1]
Platforms PDP-8
Kernel type Time-sharing operating systems
Default user interface Command line interface
License Proprietary

TSS-8 is a discontinued little time-sharing operating system co-written by Don Witcraft and John Everett at Digital Equipment Corporation in 1967. 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). [2]

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.[3]


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. [4]

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.[5]

Historical notes[edit]

  • TSS/8 sold about 100 copies
  • 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)." [6] [7]


  1. ^ OS history
  2. ^ p.180,COMPUTER ENGINEERING" (C)'78 by DEC/Digital Press. C.Gordon Bell, J.Craig Mudge, John N. McNamara, ISBN 0-932376-00-2
  3. ^ FAQs
  4. ^ https://raymii.org/s/articles/Running_TSS_8_on_the_DEC_PiDP-8_i_and_SIMH.html
  5. ^ FAQs
  6. ^ http://www.computer.org/csdl/trans/tc/1969/11/01671170-abs.html
  7. ^ http://research.microsoft.com/en-us/um/people/gbell/CGB%2520Files/Design%2520and%2520Behavior%2520of%2520TSS8%2520IEEE%25206906%2520c.pdf
  8. ^ p.181,COMPUTER ENGINEERING" (C)'78 by DEC/Digital Press. C.Gordon Bell, J.Craig Mudge, John N. McNamara, ISBN 0-932376-00-2