> actually, aside from IIRC the VAX {7,10}000, all VAXen have a 512M
> physical limit.  it's because of the page format, they cant support
> more than that without some hacks.

That doesn't sound right.  The VARM, at least the version I've got (rev
6.1, 20 May 1982) specifies 21-bit physical page numbers, which makes
for a 1G physical limit.  Now, of course, I/O space has to come out of
that, but that isn't more than several megabytes, at least not on the
buses I'm familiar with - are there really machines that demand half a
gig for I/O space?

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