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Why does Ubuntu only show 3GB of RAM?

I recently upgraded my system from 2 to 4 GB of memory. When I booted into Ubuntu, it's only recognizing 3 GB.

I followed some instructions on adding the PAE; now when I boot up my kernel has switched from generic to PAE but I'm still only showing 3 GB. How do I get it to read all 4 GB?

I went to the Software Center and found the PAE, then when I clicked "More info" it shows a few more packages with it but they aren't checked. Should I check them to be added also? Will this make Ubuntu recognize my 4 GB?

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marked as duplicate by Jorge Castro, Mik, Mitch, maythux, devav2 Oct 11 '12 at 5:56

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
Is this relevant at all? askubuntu.com/questions/20571/… –  Caesium Feb 23 '12 at 14:22
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Does cat /proc/cpuinfo | grep pae (in a Terminal) produce any output? If it doesn't print out any output then your CPU is not pae-capable and is therefore not able to address more than 3GB of RAM. –  Githlar Feb 23 '12 at 14:32
    
Can you please post screenshot of disk utility? –  Tachyons Feb 23 '12 at 15:44
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@robert The red color is just there to highlight the search term you supplied to grep. The fact that pae is listed at all, in any color, means that your CPU does support it. –  ændrük Feb 29 '12 at 1:50
    
Does your motherboard have on board video? When you don't have a separate video card, some of your main memory is allocated for video. The amount is controlled in the BIOS. –  fragos Feb 29 '12 at 7:36

3 Answers 3

To start with, what version of Ubuntu have you installed? 32bits or 64bits? If I'm correct 32bits systems won't be able to use more than 3Gb of memory, try with the 64bits version.

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That's why people are suggesting to use the PAE kernel; this allows using more than 3 GB on 32-bit. –  roadmr Apr 23 '12 at 15:18
    
But then why not use the 64bits directly? –  Victor P. Apr 23 '12 at 18:57
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PAE is useful on systems that can't handle the 64-bit version of Ubuntu (i.e. no x86_64 support). Also, 64-bit-compiled binaries are larger and a 64-bit system will "use" more memory. Using the PAE kernel is a good way to take advantage of extra memory while sparing the user having to reinstall the whole system. Nevertheless, the assertion that 32-bit systems won't be able to use more than 3GB is incorrect. –  roadmr Apr 23 '12 at 19:00
    
As I had commented earlier on here I bought a new computer and installed the 64 bit.I had been running the 32 bit and added the pae but still no luck.my new system has ubuntu as only OS and 64 bit. –  robert Apr 23 '12 at 19:10
    
Oh yeah the 64 bit recognizes all 8 gigs –  robert Apr 23 '12 at 19:10

You said

lshw -short -C memory and it seems that ubuntu is showing that I can have a maximum of 4 gigs but still only reading 3 gigs.

Why do you say it is only reading 3 gigs? What do you mean by "reading"? What command are you using that shows it is "only reading 3 gigs?" My guess is that your system is recognizing all 4 GB.

The easiest command you can use to confirm this is:

top

Here is what mine shows on a 4GB system with 64 bit Ubuntu:

Mem: 3930080k total,

Here is another well-used command:

$ cat /proc/meminfo

Mine shows:

MemTotal: 3930080 kB

You can also try:

dmesg|grep Memory

Or, if you install the hwinfo package, run it:

hwinfo

Finally, if you really don't see around 4GB from those commands, and the difference is not due to an onboard video card, here is a similar question: Ubuntu detects only 3.2GB RAM on a 64bit OS

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@MountainX-I say reading basically because through every command you just posted I got 3 gigs read by ubuntu.My bios detected all 4 gigs.As I stated here I added the 64bit pae to my 32 bit version of ubuntu 11.10.I couldnt figure it out but no worried I sold that computer and bought a new.I installed ubuntu 64bit as my only os and it reads all 8 gigs –  robert Apr 18 '12 at 14:16
    
also,I was running an ati x1050 card pci standalone but my new computer doesnt even have onboard –  robert Apr 18 '12 at 14:17
    
ok, enjoy your new computer! –  MountainX Apr 19 '12 at 2:34

I believe your motherboard does not support more than 3GB of RAM. Which board do you have?

This article has some pretty good info: http://en.wikipedia.org/wiki/3_GB_barrier

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1  
-the mobo supports 4 gigs as in the bios the 4 gigs is recognized –  robert Apr 18 '12 at 14:12

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