Dan Nelson wrote:
In the last episode (Nov 17), Chuck Swiger said:
EM64T uses 64-bit wide registers and addressing, and can talk to >4GB
of RAM natively. Older processors may still support >4GB of physical
RAM using the PSE/PSE-36 CPU extensions, but are still using 32-bit
registers.
PAE/PAE36, right? Note that if you enable PAE, some drivers may not be
available. See the PAE kernel config file for a list.
PAE is related, but I don't believe "PAE36" exists; cpuid lists these:
PSE Page Size Extensions
PAE Physical Address Extension
PSE-36 36-bit Page Size Extension
I believe PSE lets you choose whether your MMU uses a 4KB or a 4MB pagesize for
virtual address translation. PAE was the first attempt at supporting more than
4GB of address space, but I gather it requires doing bank swapping or something
fairly awkward that doesn't play too well with VM, whereas PSE-36 integrates
more easily.
The other point you've made is correct, that is, a fair number of drivers don't
understand PAE/PSE36 yet, and will not work using it-- generally because the
hardware associated with the driver has a DMA engine which is limited to 32-bit
addressing. You end up having to double-buffer or use "DMA bounce buffers",
whatever phrase you wish to use. :-)
This link seems to have a more complete description:
http://www.microsoft.com/whdc/system/platform/server/PAE/pae_os.mspx
--
-Chuck
_______________________________________________
freebsd-questions@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-questions
To unsubscribe, send any mail to "[EMAIL PROTECTED]"
