Ian, cromewell, prae, too, jim, dcs, geoff, D, anyone!...can anyone answer this pae?

apj101

apj101

VIP Member
Ok there have been about a dozen threads in the past month asking about why you can only see 3.xGB of ram in a 32bit os (vista or xp)
Now we all know the reason why is due the OS having to address all other things on the pci (mainly the gpu ram).
so you never get the full 4gb of main board ram

my theory is that enabling pae on such a rig would allow the OS to address all the requirement of the pci and still address all 4gb. I cant test this and I can't find a straight answer on goggle.

I know that there is probably quite a big overhead penalty with the os having to map software requests under the 32 bit address table to the 36bit address, which may negate any performance increase (if any)...but still it should work right.
 
yes, the idea with pae is to go beyond 4G. By default, the lost ram is hidden behind the memory mapped io, and cannot be used. If supported by hardware, some of the ram can be remapped (this is done in hardware, not by windows).

BUT:

http://technet.microsoft.com/en-us/library/bb457155.aspx

"the kernel memory manager ignores any physical address above 4 GB"

Both xp and vista does this, so even if you enable pae (you do that do get support for dep), ram remapped above 4G will be inaccessible.
 
It will work perfectly on their server editions, linux can also go up there. There is not much performance lost by doing it (there might be some problems with dma, but that is another issue)
 
Just in case you don't feel like reading the link, tyttebøvs is right. Since 32bit XP/Vista will only use 4GB of address space PAE wont make all the RAM addressable.
 
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