From: Finn Thain (fthain_at_telegraphics.com.au)
Date: Sat Feb 08 2003 - 19:27:18 PST
> > ...ATA backed VM?
>
> This is feasible. I just don't think the system really needs it, except
> on MP2000s.
Is this because the CPU speed of the MP2000s is able to make better use of
more heap? Or is ATA throughput too slow on older models? Or is NOS 2.1
needed?
I was actually thinking of those NOS2.0 newtons that have quite limited
memory (like my MP120 :) An ATA card large enough to be partitioned into
extra heap as well as normal Newton stores would be a help even on those
models.
> > The only issue is what should happen once the ATA card has been
> > removed.
Yes. Swapping cards would not be an option. If removed by accident,
perhaps a message blitted to screen memory, a bit like the "Please insert
the disk" alert in MacOS? Some mechanism would be needed to ensure that
the correct card was reinserted.
> Actually, what is required is to go to supervisor mode. Currently this
> isn't possible unless we design a system patch letting us go to
> supervisor mode.
Can the NOS extend it's heap dynamically in supervisor mode? I have only a
cursory understanding of VM operation, but it seems to me that to extend
the heap, you would need a page fault exception handler that could access
the ATA backing store... but I guess you already have a good insight into
that problem :) Could it be that ATA cards are already memory mapped?
--Finn
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