>>> 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 [...] 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, [...]
> IO space starts at 512 megs, as ragge has posted.

But that's not a VAX architecture limit, it's an implementation
decision, right?  Not "because of the page format", but rather because
the designers of the implementation in question decided to give up RAM
space for something else, probably simpler decoding logic in the
physical memory interpretation circuits....

Not that a half-gig of RAM isn't enough; I'd love to have that much in
my VAX.  But I think that dream will remain just that, a dream; "my
VAX" is a MicroVAX-II. :-/  (I have another VAX, a VS4k if memory
serves, but it appears to be broken.)

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