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Installed memory ≠ usable size?

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Special Forums Hardware Filesystems, Disks and Memory Installed memory ≠ usable size?
# 22  
Old 07-16-2009
BIOS and Video RAM allocation

The blog you linked to noted that PCI-Express controllers can allocate 512 MB of address space. This might be what's happening, and the controller is allocating the upper part of the 32-bit memory address on the bus. Take out your video controller, and put in a generic PCI one (or use the motherboard's generic one??) In fact, take out ALL PCI-E controllers. Maybe the allocated memory will change.

The second thing to try -- not at the same time as above, please -- is specifying mem=4096M on the kernel line in grub. Go to grub.conf and change this, or on boot, append that option to the kernel-load line. Maybe the OS will magically remap whatever is eating the address space and see 4GB. Then, make sure you try to ALLOCATE that memory, to make sure it's actually usable. A simple perl script will do the job.
# 23  
Old 07-16-2009
Curiosity got the better of me. I downloaded and read the user manual for this motherboard.

It is a dual channel memory architecture which supports 4 x DIMM, Max. 16 GB, DDR2 1066/800/667 ECC, Non-ECC, Un-buffered Memory.

It has an integrated ATI Radeon™ HD 3300 GPU with onboard 128MB DDR3 1333 memory and supports a maximum shared memory of 512MB

In the Advanced/Internal Graphics Configuration menu, there is an option to adjust your UMA Frame Buffer Size. Options are auto, 32MB, 64Mb, 128Mb, 256Mb, 512MB.

CRGreathouse, my betting is that yours is set to auto.
# 24  
Old 07-16-2009
Wow, many good suggestions all at once!

Quote:
Originally Posted by otheus
The blog you linked to noted that PCI-Express controllers can allocate 512 MB of address space. This might be what's happening, and the controller is allocating the upper part of the 32-bit memory address on the bus. Take out your video controller, and put in a generic PCI one (or use the motherboard's generic one??) In fact, take out ALL PCI-E controllers. Maybe the allocated memory will change.
I'm using the motherboard's generic one, and that didn't fix it. Good thought, though.

Quote:
Originally Posted by otheus
The second thing to try -- not at the same time as above, please -- is specifying mem=4096M on the kernel line in grub. Go to grub.conf and change this, or on boot, append that option to the kernel-load line. Maybe the OS will magically remap whatever is eating the address space and see 4GB. Then, make sure you try to ALLOCATE that memory, to make sure it's actually usable. A simple perl script will do the job.
I will try this in a bit. That sounds like it could be the problem!

---------- Post updated at 07:12 PM ---------- Previous update was at 07:10 PM ----------
Quote:
Originally Posted by fpmurphy
In the Advanced/Internal Graphics Configuration menu, there is an option to adjust your UMA Frame Buffer Size. Options are auto, 32MB, 64Mb, 128Mb, 256Mb, 512MB.

CRGreathouse, my betting is that yours is set to auto.
Ooh... let me check that. I remember seeing that setting, but not how I left it.

I'm going to have to look that one up to better understand it. I don't properly understand why that would affect me at 4 GB but not at 2 GB. Any thoughts?
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