Just got a Dell XPS Gen 4 system and have been installing Fedora 3 on it. I believe the chipset is an Intel i925X/XE, and it has 4 gigs of ram. The BIOS recognizes all 4 gigs, but Fedora only seems to see 3 gigs of it. I've moved around the DIMMS to see if one was acting funky, but that didn't change anything.

Interestingly, memtest86 v3.2 also only sees 3 gigs.

Any thoughts? Thanks!

I have exactly the same problem. I was running FC2 with 2GB of RAM and all was OK. Then I installed an additional 2GB. The BIOS now sees 4GB but linux only sees 3GB as seen by the 'free' command, the 'top' command, and also the 'system monitor'.

Specs:
Fedora Core 2
Kernel: 2.6.5-1.358
Dual Xeon 3.2GHz (Nocona)
Tyan Thunder i7525 (S2676) mobo
4 modules of 512KB DDR2 Corsair originally
Added 2 modules of 1GB DDR2 Corsair

You need to recompile the Fedora kernel and add the option to support 4gb ram and above.

Thanks, I did find some other posts on this topic, something about the enabling "highmem", which can be found int the "Processor type and features -> High memory support" section of the compiler options, and then recompiling the kernel. I'm not that familiar with kernel compilations, would this stuff be found when you run 'make menuconfig' in /usr/src/linux (or similar directory)? Can something like this be achieved simply by passing an option to to the compiler at boot time, say, by editing grub.conf? I can't try these things right now as my system is too busy.

Nothing I know of can be passed at grub since the kernel is only knowing what is compiled with at time of build. Check out this post on kernel compile. It is quite easy to do with Redhat / Fedora Core setups. http://www.linuxquestions.org/questi...36#post1401136

Some of the steps are for help to others but I believe it can be followed. For you you need to change a value under the Processors typeand features. I would go with 64meg here myself.

Brian1

I tried rebuilding the kernel in order to enable 'High Memory Support' so that linux would detect all 4GB of RAM instead of only 3. When I ran make menuconfig, I looked in the section 'Processor type and features' but found no 'High memory support' option.

NOTE: I am running the x86_64 version of linux as I heard it supports some special features of my Nocona chips.

Specs:
Fedora Core 2, x86_64
Kernel: 2.6.5-1.358 (smp enabled)
2 Xeon processors, 3.2GHz Nocona
4 GB RAM installed (BIOS detecs all, linux detecs 3 GB)
Tyan Thunder i7525 (S2676) mobo

Here what I see in make menuconfig, in 'Processor type and features -->'

Processor family (Generic-x86-64) --->
< > /dev/cpu/microcode - Intel CPU microcode support
<*> /dev/cpu/*/msr - Model-specific register support
<*> /dev/cpu/*/cpuid - CPU information support [*] MTRR (Memory Type Range Register) support [*] Symmetric multi-processing support
[ ] Preemptible Kernel [*] K8 NUMA support
(8) Maximum number of CPUs (2-8) [*] IOMMU support

Am I doing something wrong?

I could be wrong but x86_64 appears to not need the high memory addressing option in the kernel. AFAICT its only needed for 32bit x86 processors with over 1gb of ram.

Also, it doesn't appear to appear in the config options for x86_64.

HTH