On Fri, 2005-06-24 at 01:37 -0400, Peter Arremann wrote:
How does that work? :-)
It works on the reality that the 32-bit Athlon and 64-bit Athlon use the _same_ 40-bit/1TiB EV6 addressing to memory (as well as tunneled over HyperTransport to other CPUs and I/O in the case of the latter). In reality, they are the same core designs too (the latter just being revamped ALU with 64-bit features, more 128-bit XMM registers and the evolution of its on-CPU AGPgart to the I/O MMU).
Normally the 32-bit Athlon is limited in its addressing to 32-bit/PAE36 (4/64GiB) for Intel GTL compatibility at the BIOS, OS, etc... If you have a BIOS that lets the 32-bit Athlon break 32-bit/PAE36 Intel GTL compatibility, and pair it with an OS that does the same, then you can have the _full_ support of 32-bit Athlon's EV6 addressing architecture. In fact, EV6 is _nothing_ like GTL, but it just emulates it. That includes it looking like a "SMP bus" in the case of Athlon MP, when -- in fact -- it's an "MP switch."
If you want to know more about the non-PAE36 >4GB Linux hack and the few Athlon MP mainboards with BIOSes that support it, read up on the LKML circa February 2004.