On Tue, Aug 03, 2010 at 09:53:48PM +0200, Soren wrote: > Heh... nice writeup, Greg, but not completely updated, if I humbly may say so. > > If one look at the MS support sites about this question, one will get as many > different and contradicting explanations on the subject, as there are support > numbers > (Qxyz). Beats the crap out of most techs that I know. > > However, I have built a large number of AV systems, and quite a number of > those are with more than 4GB RAM, even up to 32GB. They all use the installed > RAM without any > problems, so I guess that at least *some* of MS's support sites are right, > when some obviously aren't. > > There is no "trickery" because the processor is not limited to 32 bits of > physical address in PAE mode. PAE mode adds a third level of page table > lookup and changes the > page table entries (PTEs) from 4 bytes wide to 8 bytes wide. This gives more > room for bits of physical page address, or "page frame number." In the first > CPUs to > implement PAE only four more bits were implemented, for a total of 24, or 36 > bits of physical address. Thereby allowing 64 GB of ram to be directly > addressed. No > "trickery" is involved. It's the same address translation the MMU has been > doing all along; the format of the lookup tables (page tables) is just > changed.
A single process cannot use more than 3GB though. http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx -- Bryan G. Seitz
