Using all of 4GB RAM... questions and Vista versus Linux...
Christopher A. Williams
chriswfedora at cawllc.com
Wed Oct 1 16:02:17 UTC 2008
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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