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Re: Using all of 4GB RAM... questions and Vista versus Linux...



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



--
==================================
By all means marry;
If you get a good wife, you'll be happy.
If you get a bad one, you'll become a philosopher.

--Socrates


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