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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.

The operating system runs on the 12-bit PDP-8 computer starting with the PDP-8I model and was released in 1968.

Authorship

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).

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.

Architecture

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.

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.

Like IBM's CALL/OS, it implements language variants:

• 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.
• 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 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.

Legacy

TSS/8 sold more than 100 copies.

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)".

The RSTS-11 operating system is a descendant of TSS/8.

References

1. ^ 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. ^ PDP-8/E PDP-8/M & PDP-8/F Small Computer Handbook (PDF). Digital Equipment Corporation. 1973.
4. ^ 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.

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