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Just installed 11.10, but it's not detecting all 8GB of RAM. System Info says there are 3.9GB. Bios doesn't have a problem recognizing all 8.

free -m

results in:

             total       used       free     shared    buffers     cached
Mem:          3957       1478       2479          0         22        687
-/+ buffers/cache:        768       3189
Swap:         4089          0       4089
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1  
can you post the output of cat /proc/meminfo ? –  Micro Dec 1 '11 at 6:01
1  
First, are you really on 64-bit? uname -a –  Uri Herrera Dec 1 '11 at 6:49
    
you probably got 32bit, not 64 bits –  Dr_Bunsen May 14 '12 at 12:30

3 Answers 3

The PAE kernel is not installed by default. You need to install the following packages:

linux-image-generic-pae linux-headers-generic-pae

using

apt-get install linux-image-generic-pae linux-headers-generic-pae

The headers are only relevant if you need to build code on the machine. If you are using a package such as build-essential this should be pulled automagically.

Hopefully this helps...

Ref: https://help.ubuntu.com/community/EnablingPAE

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Ok. Feel free to edit or suggest edits, sorry –  hexafraction May 14 '12 at 12:19

Just copy this to the terminal, and hit enter, to write your password: sudo apt-get install linux-generic-pae and after reboot, your problem will be solved.

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3.9 GB is the limit for 32-bit, you probably installed the wrong version. If you are indeed running 64-bit, the uname -m command should output x86_64.

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this is not true, practically every recent release of Ubuntu uses the PAE module for the kernel when a 32 bit is used on a machine with more than 3.5Gb of RAM, so this is not a valid explanation –  Micro Dec 1 '11 at 6:04
2  
The PAE kernel is not automatically installed, @Micro. In most Ubuntu Desktop situations, its not installed by default. The last release that I saw which by default installed the PAE kernel over the non-PAE kernel was 10.04.0 LTS. Every release since, I have yet to see it auto-install the PAE kernel. So Dalton's statements are somewhat correct to that extent. –  Thomas W. Dec 1 '11 at 6:42
    
in my experience the PAE module is always present, i never ever experienced a 32 bit installation without the PAE module, at least this is true for me since lucid. –  Micro Dec 1 '11 at 6:50
    
@Micro: and yet he is right, 4 GiB is the limit for 32bit. PAE actually adds bits internally, thus his assertion is right, albeit somewhat incomplete. –  0xC0000022L May 14 '12 at 12:16

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