[rhelv6-list] RHEL6 x86 on system with 4 GB memory

[Lamar Owen]

On Tuesday, May 10, 2011 03:20:08 PM Musayev, Ilya wrote:
> Had exactly the same issue on Dell Desktop ~4 years ago (dont recall the specifics).
> 
> I upgraded the BIOS, but still it was the limitation of the BIOS to present the 4GBs to OS. After loading up PAE kernel running Fedora 6 with some tweaks, i was able to get more memory from the box. Initially i had 3.3 and it went to 3.7GB. 
> 
> Long story short, it was vendor/model specific issue for me and not so much kernel/OS.

Resurrecting an old thread for the second time...

It's chipset related.  For instance, a Dell Lattitude D820 has the Intel 945 chipset; the D830 has the 965.  

The 945 that's in the D820 (also Precision M65) is unable to address beyond 4GB period, PAE or no PAE, and chipset support is required for the CPU to do it (and since the PCIe devices require address space, the memory hole under that address space isn't usable, much like in the old Xt and AT real mode architecture where even if you had 1MB of RAM you could only get 640K normally, and somewhat less than 1MB with UMB mapping support, and the HMA with A20 handler support added just short of 64K above the 1MB ).  

The 965, at least in the D830, can address above 4GB, and you can get the full amount with remapping support to get the RAM normally shadowed by the PCI/PCIe address space mapped above the 4GB (32bit addressing) line.  Look for the BIOS option relating to the 'memory hole' or similar remapping.  Then the PAE support in the CPU can access A32-A35 and get at the rest of the memory.