Subject: RE: current on vax
To: 'Johnny Billquist' <bqt@update.uu.se>
From: Antonio Carlini <arcarlini@iee.org>
List: port-vax
Date: 11/20/2003 00:50:55
> I wonder if it might have to do with the fact that the 7000 
> machines can have up to 3 gig of memory (was it 3 gig?), 
> compared to older machines who were limited at 512 meg (or 
> whatever). (I'm not sure if the 6000-6xx machines were in the 
> large memory family or
> not.)

The XPA/XVA project did lead to systems that could address
4GB, with 0.5GB still kept for I/O space. The VAX 7000 systems
could do this. So could the VAX 6000-600 systems. The VAX 6000-500
systems did have some expanded addressing capability, but I think
that was restricted to 1GB or so. I don't think it ever was supported
(or even mentioned). I don't know whether it is possible to
activate this support (or even stuff enough memory in the available
slots ... I'd have to dig through some manuals). I think the
VAX 9000 also had this capability, but it was decided that 
supporting it would be uneconomical (so it pretty much
matched up to the rest of the machine :-)).

The extended addressing did have some impact on devices. The XMI/BI
adapter (XBIA - DWMBA ?) needed to be enhanced and became the
XBIA+ (DWMBB?). The DMB32 driver needed to change to run the card
in a different mode, since it had deep knowledge of PTEs and
such like in most of its addressing modes. There were doubtless
other changes to other drivers and hardware.

Antonio
 
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Antonio Carlini             arcarlini@iee.org