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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