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

From: Paul Koning <>
Date: Sat Oct 23 12:39:31 2004

>>>>> "Graham" == Graham Toal <> writes:

>> Interesting -- DOS format magtape. 6.3 filenames... Some of the
>> command files on that tape look like RSX ones, and some are RSTS
>> ones. Makes sense; compilers and things like that built for RSX
>> generally run just fine on RSTS (in RSX emulation).

 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).

Received on Sat Oct 23 2004 - 12:39:31 BST

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