hollaar@utah-cs.UUCP (Lee Hollaar) (09/25/87)
In article <819@sugar.UUCP> peter@sugar.UUCP (Peter da Silva) writes: >In article <1745@ncr-sd>, greg@ncr-sd (Greg Noel) writes: >> In article <8490@think.UUCP> rlk@THINK.COM writes: >> >.... The PDP11 didn't have virtual memory either, >> >if my memory serves me. .... >> >> At the risk of re-opening an old debate, the PDP-11 \does/ have virtual >> memory. It's just that, for various technical reasons, the original Unix >> implementation for it chose to use swapping instead of paging as its virtual >> memory technique. > >And neither did any other operating system for the PDP-11 (RSX, RSTS, RT-11), >probably because it didn't in fact have the capability of supporting VM. >Why do you think DEC developed the Virtual Address Extension (VAX) in the >first place? > >-- >-- Peter da Silva `-_-' ...!hoptoad!academ!uhnix1!sugar!peter >-- 'U` Have you hugged your wolf today? >-- Disclaimer: These aren't mere opinions... these are *values*. While none of the DEC-supplied operating systems supported virtual memory, there was at least one operating system that did. It was called DURESS (as in "I'm running my program under DURESS"), and was developed by a strange group in Champaign, Illinois, for Datalogics, a Chicago company that builds high-quality typeset systems. It was based loosely on DEC's DOS (that's where the assembler and compilers were from), and ran on one of the first PDP-11/45's delivered. It not only supported virtual memory, but even separate instruction and data spaces to give twice the address space for a program. It also ran on the PDP-11/70 and a PDP-11/45 with a specially-designed memory management card to allow for 2 Megabytes of memory. To run it on a PDP-11/44, you had to modify the processor to add a gate, because DEC overlooked something when they designed the 11/44, and you had trouble if there was a page fault when jumping to a new instruction location. DEC probably went to the VAX addressing to get around the address space limitations of the PDP-11, but it certainly wasn't necessary to support virtual memory, if you knew what you were doing and didn't mind a little pain. Lee Hollaar ps. I managed the group that built DURESS, so I do know what I'm talking about.