Claude Jones wrote:
On Tue August 26 2008 10:52:21 am Roger Heflin wrote:
Don't count on that, the 4GB thing is a very very rough and
often wrong *SIMPLE* rule.
Just because a machine has under 4GB of ram does not mean that
the PAE kernel won't give you more memory. The bios *CAN*
(some do, some don't) remap something that is covered by a
video card, or otherwise reserved for something to above 4GB
requiring a PAE kernel to use it. And this can start
happening at around 3GB of ram or more, the only way to know
if PAE is correct for a given setup is to either know exactly
what the bios is doing or to test it.
It all depends on exactly what the bios is doing, he would
need to boot a PAE and a non-PAE kernel and check how much
memory is being seen by each, if they are the same or really
close (within 100MB) I would avoid the PAE kernel.
Interesting... I'll make this a keeper and test soon. I build
most of my machines with 4GB of ram now, but that's in Windows
land at work - they tend to filter my way as older ones are
superceded or retired - my current Linux machines all top out at
3GB
If the bios maker *ONLY* worries about having max ram with 32-bit
Windows, then it is likely that the did not remap above 4GB,
but sometimes there is a bios option to change this behavior
to work better for Linux and/or 64-bit windows. Given that windows
is changing then it becomes more likely for them to be remapping
above 4GB. If they don't remap above 4GB they will maximize the memory usable
for 32-bit windows (depending on the exact hw, they may have to remap
larger amounts than are actually covered and that would lower the ram usable
under 32-bit windows, so no remap is better for 32-bit windows in this case),
but a proper remap would allow anything using PAE (I thought the server versions
of Windows did use PAE) or 64bit to have more ram that without the remap.
And of course it all depends on exactly what the bios engineer for the MB
company decided to do, and often it depends on what they classify the
motherboard as, server boards and boards that support more than 4GB are
more likely to have the options to do remapping as they already expect
someone to be using either PAE or 64bit.
Roger
--
fedora-list mailing list
fedora-list@xxxxxxxxxx
To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
