Howard Wilkinson wrote:
I am looking for a definitive answer to the question of where the PAE
kernels become useful. I have seen various articles that mention needing
PAE kernels if you have more then 4GB of physical memory in a 32-bit
processor environment. I have also seen statements that say you need
them if you have 4GB or more of memory. Now which is right? Also, even
if you need a PAE kernel because the last few bytes are not addressable
when you have exactly 4GB is this useful or is the trade off of larger
page tables and pages going to eat any benefit of being able to address
these few bytes and if so when does the PAE kernel become useful?
Howard.
It depends on the bios, you would have to try with and without the PAE kernel
and see if the amount of usable ram changes.
Some bioses won't remap any memory below 4GB (that is covered by something else)
to over 4GB, if your bios does not remap anything above 4GB when you only have
4GB (or less) then PAE won't buy you anything. And since often moving the
covered memory from below 4GB, sometimes means moving some non-covered memory
and therefore lowering the memory usable for an OS that does not support PAE-ie
that other OS, often the bios *WON'T* move the covered memory at all because it
would lower the usable memory below 4GB for that other OS.
This is almost always true on the Desktop class MB's, and it is sometimes true
on the higher end stuff also.
Roger
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