On Mon, Mar 23, 2020 at 1:30 PM Robert Armstrong <b...@jfcl.com> wrote: > > > Johnny Billquist <b...@softjar.se> wrote: > >The memory bus on the VAX-11/750 is the same as for the MK11 box for the > >PDP-11/70, and they shared some memory cards. > > Same memory was used on the 730 too. The 730 memory cards were always 1MB > though - never saw any other size.
Yes. The 11/70 supported the 256K cards only, the 11/750 supported either the 256K cards or the 1MB cards (early 11/750s lacked one address wire on the memory bus - I added it to our machine S/N BT0000354), and the 11/730 (and 11/725!) supported only the 1MB cards, but I don't know if that was because of memory controller limitations or because you could only stuff 5 cards in the box and 1.25MB wasn't enough to run VMS. > I don't know the actual number of physical address bits implemented on the > 730, but as a practical matter 5x 1Mb cards was the most you could fit in the > chassis. I remember looking into this a few years back - ISTR the PALs only generate 5 memory select lines (that go to each memory-capable slot) and there were no unused pins on that PAL. It seems possible to rework this, but I don't think it would be a trivial mod. An 8MB 11/730 wouldn't be all that much better than a 5MB 11/730. Some. I remember using ours as mostly a single-user machine in the late 80s because by the time a third person logged in, it started swapping like a fiend. -ethan _______________________________________________ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh