Some PDP-11 info (was Re: C compilers for RSTS/E?)

Which reminds me... students at Groningen University wrote a multi-tasking system for the PDP that was loosely based on EMAS (big mainframe system of the OS was that it used an RT-11 format disk structure for raw storage even though the user view of files was quite different. For example I think RT-11 had version numbers (in the style of VMS), but GUTS showed only the top-level file, and had a "pop" command which deleted the most recent file and made the version below it visible. The source is lost (though we do have a disk pack which *may* contain the OS, if it is still readable) but a scan of the three-book report is available online: http://history.dcs.ed.ac.uk/archive/scans/guts/ - Orange is the users guide; Red - system design; Yellow - selected source listings. Edinburgh was also fairly big on PDP11's, having written a few operating systems for it. The british networking operations ran on PDP11's for years, on an O/S called DEIMOS. (Binary disk images online at http://history.dcs.ed.ac.uk/archive/os/deimos/ ; sources also at http://history.dcs.ed.ac.uk/archive/os/emas/emas2/deimos/ - the binaries ought to work in an emulator; I haven't tried them myself) Deimos was also used for the front-end terminal servers at Edinburgh, and as the basis of the Edinburgh Remote Terminal Emulator (ERTE) which submitted jobs as if they were typed by remote users, to do accurate performance monitoring without the Heisenberg interaction of measuring the performance on the system itself. This has no relation to the 'fuzzball' arpanet routers, written by David Mills (of NTP fame) who was also at Edinburgh at the time. Another PDP/11 O/S was "MUSS". There's a manual page for it here: http://history.dcs.ed.ac.uk/archive/os/emas/users/ercm09/emas-2900/docum_mm… I think the sources of MUSS along with the FEP's and ERTE are in that directory somewhere too. DEIMOS, MUSS, ERTE and the FEPs were written by Brian Gilmore, now head of the Computing Service. Ian Young wrote an operating system for the PDP-11 called "rats" as a student project - I believe he has a paper listing which we might have scanned some day. That was the first implementation of lightweight threads that I remember seeing. All the Edinburgh software was written in Imp, except for a few assembler parts, but we had our own assembler for it as well: http://history.dcs.ed.ac.uk/archive/os/emas/users/ercm09/emas-2900/asst11j.… There were two compilers for the system; one written by the ERCC based on a simpler bootstrapping compiler called "SKIMP" - http://history.dcs.ed.ac.uk/archive/languages/imp11-tmp/imp11/sk11v.imp ... and a later one written by the Computer Science department for the Imp77 language: http://history.dcs.ed.ac.uk/archive/os/emas/users/ercm11/emas-a/imp119s/ (and a very early version of the above, we think: http://history.dcs.ed.ac.uk/archive/languages/imp11-tmp/earlyimp11/ ) There's a good writeup of the pdp-11 imp compiler optimisations here: http://www.gtoal.com/athome/edinburgh/imp/PDP11IMP.htm Graham