Re: memory remapping, 4gb memory on 945gt

H. Peter Anvin
2008-01-04T22:05:00Z

Dr. David Alan Gilbert wrote:
>>>
>>> Now I can understand this explanation for 32-bit mode, but I'm running
>>> in 64-bit mode. There should be a way to use the fourth gig under
>>> Linux. Is there?
>> The chipset limitation applies to 64bit mode as well as to 32bit mode
>> (which actually does not have a 4GB limitation with PAE)
>
> Note that some system and memory vendors have incorrect statements
> stating that the 3.xGB limit is a 32bit OS issue on these machines
> and it'll all just work fine on 64bit OSs.
>

Supposedly WinXP-32 doesn't use memory over 4 GB even if it is available
(a market-segmentation decision of the part of Microsoft, to force
people to buy WinServer 2003; WinXP SP2 does PAE so there is no
technical reason.) This probably has disincentivized hardware vendors
from providing support for remapping the memory from the aperture above
the 4 GB mark. The logic isn't all that trivial, especially if the
aperture size is configurable, so I can understand why they would punt.

-hpa