4 GB RAM showing up as 3, BIOS memory hole and all that

Martin Cracauer cracauer at cons.org
Tue Aug 16 15:14:33 GMT 2005

> You are definitely going to loose the address space from 3.75GB to 4GB
> to normal PCI and APIC overhead.  If you have PCI Express then you'll
> likely also loose the space from 3.5 to 3.75GB.  Any other space lost
> beyond that would be possible but usual.  And no, most AMD systems do
> *NOT* remap the lost space.
> If you want a detailed analysis then please send a verbose boot message
> along with a pointer to the specs on your motherboard.  That will give
> enough to information to say if FreeBSD is at fault or if your
> motherboard is simply sub-standard.

If you have time for explanations I would rather be interested to know
how the above situation works in the case that you *don't* have 4 GB
of RAM.

Correct me if I'm wrong but:
- the above 3.5 to 4.0 GB addresses are physical, not virtual
- if you have less than 3.5 GB there is no physical memory at these
  addresses that PCI and APIC need
- but if you have 4 GB there is physical memory at these addresses

I don't understand how this can transparently work with and without
physical RAM at 3.5-4.0 GB.

I am not worrying too much about my particular board, and in any case
I just fatfingered a BIOS update and it won't POST :-)
It's a Arima Rioworks HDAMB http://www.rioworks.com/HDAMB.htm If
people are interested I can send the boot -v afer I recover.

Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/
 No warranty.    This email is probably produced by one of my cats 
 stepping on the keys. No, I don't have an infinite number of cats.

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