# TSS/8

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**TSS/8** is a discontinued [time-sharing](/source/Time-sharing) [operating system](/source/Operating_system) co-written by Don Witcraft and John Everett at [Digital Equipment Corporation](/source/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](/source/12-bit) [PDP-8](/source/PDP-8) computer starting with the PDP-8I model and was released in 1968.

## Authorship

TSS/8 was designed at [Carnegie Mellon University](/source/Carnegie_Mellon_University) with graduate student Adrian van de Goor, in reaction to the cost, performance, reliability, and complexity of IBM's [TSS/360](/source/TSS_(operating_system)) (for their [Model 67)](/source/IBM_System/360_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](/source/Teletypewriter)) handler and 680-I service routine for TSS/8.

Roger Pyle and John Everett wrote the [PDP-8](/source/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](/source/PDP-6) and [PDP-10](/source/PDP-10), wrote an expanded version, PAL-X, for TSS/8.[5]

## Architecture

This timesharing system is based on a protection architecture proposed by Adrian Van Der Goor, a grad student of [Gordon Bell](/source/Gordon_Bell)'s at [Carnegie-Mellon](/source/Carnegie_Mellon_University). 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](/source/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](/source/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](/source/BASIC-8) programs are limited to 350 lines, but "chaining" allows "programs of virtually any length." BASIC-8 is based on [Dartmouth BASIC](/source/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](/source/FOCAL_(programming_language)), which has been available from earlier PDP/8 models and it provides an algebraic language as well as a desk calculator mode.

## Legacy

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](/source/RSTS/E) [operating system](/source/Operating_system) is a descendant of TSS/8.[4]: 181

## References

1. Remy van Elst (July 26, 2015). ["Running TSS/8 on the DEC PiDP-8/i and SIMH"](https://raymii.org/s/articles/Running_TSS_8_on_the_DEC_PiDP-8_i_and_SIMH.html). *Raymii.org*

1. ["PDP-8 Digital Software News"](http://bitsavers.org/pdf/dec/pdp8/softwarenews/197603_PDP8swNews_DEC-08-XSMAD-A-D.pdf). March 1976. DEC-08-XSMAD-A-D.

1. [*PDP-8/E PDP-8/M & PDP-8/F Small Computer Handbook*](http://www.bitsavers.org/pdf/dec/pdp8/handbooks/Small_Computer_Handbook_1973.pdf). Digital Equipment Corporation. 1973.

1. C. Gordon Bell; J. Craig Mudge; John N. McNamara (1978). [*Computer Engineering: A DEC View of Hardware Systems Design*](http://bitsavers.org/pdf/dec/_Books/Bell-ComputerEngineering.pdf). [Digital Press](/source/Digital_Press). ISBN 0-932376-00-2.

1. ["Who's Who?"](http://www.faqs.org/faqs/dec-faq/pdp8/section-15.html). *PDP-8 Frequently Asked Questions*

1. ["What operating systems were written for the PDP-8?"](http://www.faqs.org/faqs/dec-faq/pdp8/section-10.html). *PDP-8 Frequently Asked Questions*

1. ["Appendix E: Implementation Notes, page E-1"](http://bitsavers.org/pdf/dec/pdp8/tss8/DEC-T8-KJZA-D-TSS-8_BASIC_8_Programming_Manual_Mar1969.pdf)

1. ["TSS/8 ALGOL"](https://groups.google.com/d/topic/alt.sys.pdp8/KUw3praLkmE)

1. 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"](https://gordonbell.azurewebsites.net/CGB%20Files/Design%20and%20Behavior%20of%20TSS8%20IEEE%206906%20c.pdf). *[IEEE Transactions on Computers](/source/IEEE_Transactions_on_Computers)*. **18** (11): 1038–1043. [doi:10.1109/T-C.1969.222577](https://doi.org/10.1109/T-C.1969.222577). [S2CID 16325116](https://api.semanticscholar.org/CorpusID:16325116)

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Adapted from the Wikipedia article [TSS/8](https://en.wikipedia.org/wiki/TSS%2F8) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/TSS%2F8?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.