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

D. Hugh Redelmeier hugh-pmF8o41NoarQT0dZR+AlfA at public.gmane.org
Fri Nov 5 13:57:04 UTC 2010


I bought an Acer Aspire Revo 3610 a couple of months ago.  It came
with 4G of RAM (as advertised).  But it doesn't make all of it
available to the OS.

I found this odd.  I figured that this was a BIOS bug.  So I bugged
Acer.  After much tooing and frowing, they said that it was a
limitation of the Atom processor.

I didn't think the Atom had such a limitation.  One reason: I have
another Atom box with 4G of RAM, all usable.  Another: that limitation 
would be dumb.

But then I read the spec sheet.  The Atom 330 has enough address pins
for 32G of physical address space.  But there is a slight hint that it
only drives enough of those pins for 4G.  That means that less than 4G
of RAM can be supported (an address window must be left for other 
devices).

See <http://download.intel.com/design/processor/datashts/320528.pdf>
Page 28 shows pins A[35:3]# but page 31 only specifies A[32:3]#.
Apparently this was a modification to the specifications.

Yuck!

My Atom box with 4G that works uses a D510 CPU.

That does not excuse Acer for advertising 4G when only 3.25G can be
used.
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