On Wed, 2008-10-01 at 08:54 -0400, Linuxguy123 wrote:
I have a new HP hdx laptop with a Core Duo T8100 processor and 4 GB
of
RAM.
$ uname -a
Linux localhost.localdomain 2.6.26.3-14.fc8 #1 SMP Wed Sep 3 03:40:05
EDT 2008 i686 i686 i386 GNU/Linux
Even though I have 4GB of RAM installed, Linux appears to only be using
3GB of it.
$ free -t
total used free shared buffers
cached
Mem: 3106944 777056 2329888 0 60608
419608
-/+ buffers/cache: 296840 2810104
Swap: 2040244 0 2040244
Total: 5147188 777056 4370132
I've read in other posts to this group that the cause of this is that
the BIOS remaps the some (1GB) of memory to serve as address space for
PCI devices, thus creating a memory "hole".
I understand that some BIOSes allow one to remap those devices elsewhere
in the map. My BIOS does NOT allow that option.
Questions:
a) On machines that do not allow PCI remapping, is the processor
physically disallowed from accessing that 4GB of RAM ? Ie have the
address lines from the processor been disconnected from that RAM due to
being connected to the PCI devices ?
b) How do XP and Vista handle this ? Are they limited to 3GB of RAM
too ?
c) I am running the 32 bit version of Linux. Would it make any
difference to my RAM access if I ran the 64 bit version ?
Overall, the issue is that you are running a 32-bit version of Linux. In
order to take advantage of the entire 4GB you need to either:
1) Run a 64-bit version
2) Run the 32-bit PAE kernel (PAE stands for Physical Address
Extensions)
At this point, it's preferable (IMHO) to just run the 64-bit version if
you can stand to re-install. You will get better results overall in
terms of performance compared to the PAE kernel and most all of the
issues around 32-bit / 64-bit compatibility have been resolved or worked
around. See the F9 release notes for details on these.
...and yes, this also applies to Windows systems. You have to run 64-bit
versions of Windows XP or Vista to see the full 4GB as well.
Cheers,
Chris
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If you get a good wife, you'll be happy.
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