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

Graham> Which reminds me... students at Groningen University wrote a Graham> multi-tasking system for the PDP that was loosely based on Graham> EMAS (big mainframe system from Edinburgh, sort of like Graham> Multics but better). I remember one feature of the OS was Graham> that it used an RT-11 format disk structure for raw storage Graham> even though the user view of files was quite different. For Graham> example I think RT-11 had version numbers (in the style of Graham> VMS), but GUTS showed only the top-level file, and had a Graham> "pop" command which deleted the most recent file and made the Graham> version below it visible. Not RT11... perhaps you're thinking of that modified system? Sounds a bit like a project I did at the University of Illinois modifying RT11. It didn't get completely finished but it worked... Changed the USR to a collection of overlays (not one big overlay). Changed the file system to allow non-contiguous files while stilll being very efficient -- roughly speaking a RT11 style fast and skinny variant of ODS-1. Named directories, but no extension file headers; LBAs limited to 2^16. I still have the sources at least on paper. The overlay stuff required some assembler hacks, to make the overlays PIC. Basically, a feature to say "this code loads at X but executes at Y". There was partial support for that, as a hidden feature, in the older Macro-11 sources but it needed work to make it flexible enough. Some other systems offered that sort of thing standard (CDC 6000s for example -- and GNU Binutils too, for that matter). paul