TSS-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 EduSystem 50.^[3]:p.2-15

The operating system ran on the 12-bit PDP-8 computer 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).^[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]

Architecture

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 notes

• 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]

References

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