On Fri, 2005-06-24 at 02:51 -0400, Peter Arremann wrote: > Hmmm - The GTL bus uses 36bit for address... So if you get a license from > Intel and build your own device, it can address 36bits directly without any > games. PAE36 is a mmu concept that allows a 32 bit OS to have 16 4GB pages > (hence the name Page Address Extensions 36 bits...) Yes, the key word there is that it "pages." BTW, it's not 16 x 4GB pages, but 120 x 512MB pages into the lower 8 x 512MB memory. Intel GTL is _still_ a 4GB platform with paging above 4GB up to 64GB. It is literally like using old EMS in DOS. > So if you have a 32 bit athlon, you get 4GB ram... To go above that, you need > more bits. Sigh ... the 32-bit Athlon uses _40-bit_ EV6. I only used the term "32- bit Athlon" to market differentiate from the "64-bit Athlon/Opteron." In reality, _both_ products use the same core with 40-bit EV6 addressing. The latter just also offers a 48-bit/PAE52 programming/register "Long Mode", whereas the former only offers a 32- bit/PAE36 programming/register mode. > Those bits need to be stored in a separate register since all your > apps and os only have 32bit 36-bit -> 16-bit segment + 32-bit offset = 36-bit (4-bits overhang). On Intel GTL, it pages above 4GB, as you mentioned. On AMD EV6, it also does it linearly in hardware for GTL compatibility. _Unless_ you have an Athlon MP mainboard with the BIOS and a Linux kernel that offers _true_ access. It that _avoids_ paging in hardware above 4GB, significantly improving performance. The Athlon64/Opteron just now have a formal mode called "Long Mode" where the 16-bit segment is the "top bits 33-48" with the 32-bit offset = 48-bit/256TiB. _Physically_ Athlon64/Opteron are still limited to EV6's 40-bit/1TiB addressing of the platform, same as 32-bit Athlon. People often get confused on _physical_ platform (board engineering- level) addressing versus _logical_ "programmer" addressing. > - and then you need to have a mmu that can combine those two into the > physical address... And the combining of an offset and a segment is > what PAE36 is all about... See where my confusion comes in? :-) Yes, reference above. > Sorry to make you even more work but I searched the LKML archives and > couldn't find anything :-( Could you please send me a direct link? I'll find it. It was from a gentlemen from AMD that discussed it in a thread right after Intel announced EM64T. Linus & co. were talking about how EM64T is still using a 32-bit platform underneath. The AMD gentlemen commented how they a few vendors had a BIOS option "Linux" for the memory access, and the Linux kernel could support linear addressing above 4GB. -- Bryan J. Smith b.j.smith at ieee.org --------------------------------------------------------------------- It is mathematically impossible for someone who makes more than you to be anything but richer than you. Any tax rate that penalizes them will also penalize you similarly (to those below you, and then below them). Linear algebra, let alone differential calculus or even ele- mentary concepts of limits, is mutually exclusive with US journalism. So forget even attempting to explain how tax cuts work. ;->