Atom 330 drives only enough pins for 32-bit physical addresses

[Lennart Sorensen]

On Sat, Nov 06, 2010 at 03:18:07PM -0400, D. Hugh Redelmeier wrote:
> "It" == ION?

The Atom 330.  I have seen references to 16GB for the Ion, but only if
the CPU supports it.

> Where did you get that information?  I have not found it with a few
> minutes of googling.
> 
> My (possibly misinformed) understanding is that the physical addresses
> go across the Front-Side Bus "in the raw".  So remapping would be the
> job of the ION chipset.  After all, memory and most other things that
> can be addressed are attached via the chipset (perhaps some CPU
> resources can be addressed without going across the FSB).

They go in the raw, but if your CPU only supports 4GB of addressing,
and the PCI bus and BIOS and other devices have to be in that 4GB,
then that's all you get.

> The remapping would be set up by the BIOS.  But it would be pointless:
> anything above 4G could not be addressed by the brain-damaged Atom
> 330.

Right.  Now the ION doesn't do remapping at all.  So even if the atom
could access more than 4GB, you would still loose some ram between 3
and 4GB, even if you had more ram above 4GB that the cpu could address.

> Why do I say brain damaged?  Because it supports the Intel FSB spec
> except for the missing (undriven) address bits.  The pins are there
> but are not driven.  This same FSB is used by Atom, Core, etc. so the
> same chipsets work with it (some newer Atoms use CMOS instead of GTL+
> signalling on the FSB).

Yeah very common for intel.

> Of course 64-bit Atoms have wide virtual address support.  Otherwise
> 64-bit operating systems would not work.  AMD64 currently limits
> virtual addresses to 48 bits and I guess that Intel 64 is the same.

I think early intel em64t were 40 bit but I think they are 48 now.

> All that the Atom can be missing is drivers for the top bits for
> physical addresses (and the very few upstream logic blocks associated
> only with them).  This smells like intentional crippling.

Very likely.

> I'm sure that at least some newer Atoms can address more memory: I
> have an Atom D510 system that does this.  It does not have an ION
> chipset.

Certainly some of the newer ones are likely to be able to.

-- 
Len Sorensen
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