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My ubuntu 64-bit 11.10 installed box has 6GB RAM but Ubuntu only uses 4.1GB.

I have read various things about the 4GB limit etc, but all those talk about using less than 4GB.

What could be causing this?

My Hardware:

  • Asus P5Q Pro
  • Intel Core 2 Quad Q6600 @ 2.40GHz x4
  • GeForce 9600GT (1024MB) Card not integrated
  • 3x 2GB DDR2 RAM Modules - PC-6400

Output of uname -a

Linux ASUS-P5Q-PRO 3.0.0-13-generic #22-Ubuntu SMP Wed Nov 2 13:27:26 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
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Do you integrated graphics? If you do some of your ram will go to that. The only way to prevent this is to get a graphics card. – TheXed Dec 5 '11 at 16:37
@TheX no I don't. Will add that to question! Meant to anyway... – neildeadman Dec 5 '11 at 16:41
Possbile Duplicate – Marco Ceppi Dec 5 '11 at 16:43
Not a duplicate as that is talking about over 3GB when I am discussing not over 4.1GB and that is because they have integrated graphics, which I don't. – neildeadman Dec 5 '11 at 16:48
Just wondering if the os isn't running on part of the ram ? ( if it's a graphical shell then i'd think that it'd take up around 500Mb or more ( especially with unity ) ) since you can't kill your os it also won't show in any processor lists and as such be "disapearing ram" ? ( just my 50 cent ) – Peter Vermeulen Dec 5 '11 at 16:50

Check in the BIOS to see if there is a setting for 32-bit & 64-bit HPET timer. I've found when the HPET is set to 32-bit, it tends to not address all of the memory available. I don't know how a timer can play in this, but make sure it is set to 64-bit. I could be reaching here, but it's worth a shot.

@jpyper on Twitter.

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Although your answer wasn't the solution... it lead me to finding the problem... so thanks! :) – neildeadman Dec 7 '11 at 8:52
up vote 1 down vote accepted

In my question above, I stated that the BIOS saw the 6GB. I said this because when booting, as it showed the device info etc before booting, it listed 6GB of RAM.

John suggested I look for a setting for HPET and in doing so, I discovered that the BIOS Setup was reporting that the only usable amount of System Memory was something like 4.3GB.

This obviously shows it wasn't a Ubuntu problem (wish I'd found this sooner!) and replaceing one of the 2GB sticks for 2x 1GB sticks gives me the 6GB I was looking for.

My memory config before was:


My configuration now is:


This only came about because I had to remove a faulty stick! But at least it's sorted now!

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This May invoke a GIYF from some. But I have tried half a dozen tricks and still my Toshiba Satelitte 630c with Ubuntu 11.10 is unable to use the 6GB (2GB + 4GB Dimm) . However, if you're to suggest conflicting freqs..its not as my Machine detects 2.3 GB of RAM... – Nocturnalknight Mar 27 '12 at 6:35
what happens if the 4gb stick is in on its own? – neildeadman Mar 27 '12 at 7:19

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