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I'm going to repeat the title in a longer word. Can a 32 bit Ubuntu address more than 4 gb of RAM on a 64 bit processor?

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8  
Is there a reason why you do not want to install the 64-bits version? –  Lekensteyn May 17 '11 at 15:39
    
64-bit programs are generally going to use more memory; up to twice as much memory in some cases. That's one good reason. –  poolie Jul 1 '11 at 15:33
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6 Answers

You need to use the PAE Linux kernel. The installer should be able to select the PAE kernel for you. Make sure that when you install, there is Internet connectivity, so that you get the PAE kernel from the start. If in doubt, you can install using the DVD ISO of Ubuntu (which definitely has the PAE kernel). For more on PAE, see Enabling PAE.

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There is a kernel option for supporting large amounts of ram. So recompiling the kernel might be an option if for some reason one doesn't want one form the repositories: linuxtweaking.blogspot.com/2010/05/… –  con-f-use May 17 '11 at 15:37
    
There are already packaged PAE Linux kernels in the official repositories, so a user should probably go for one of those. –  user4124 May 17 '11 at 16:11
    
@con-f-use that kernel options IS PAE, ubuntu already has a precompiled PAE kernel in the repositories. –  crasic May 20 '11 at 19:08
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32-bit Ubuntu will automatically install PAE kernel if it detects 4GB RAM or more. You don't have to do anything at all about it. PAE kernel can address up to 64GB RAM. The performance penalty introduced by PAE is insignificant.

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Like everybody wrote, the system as a whole can use more than 4 GB with PAE. But each process can only address 4 GB.

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+1 that's a good point! –  Takkat May 19 '11 at 12:38
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Yes it can. I am running exactly the configuration you are asking for without any problems. Obviously you need to use the PAE kernel.

However, you should think about if it is better to run the 64bit kernel since it allows to use the CPU more effectively. It depends on what you are intent to do with the computer if a 32bit kernel or a 64bit kernel is more efficient.

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How does it use the CPU more effectively? –  poolie Jul 1 '11 at 15:33
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For what i have learn, if you install the 32Bit Ubuntu on a PC that has more than 4GB or Ram it will automatically switch to PAE Mode so it can use the additional memory. There is no need to enable it since it does it automatically when it sees you have more than 4GB of ram.

For the performance of using PAE do not worry about it since the difference between it and the normal 32bit is less than 2% when using the memory above the 4GB. When using the memory in the 4GB range it will be the same performance.

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With PAE you can do something like that, but this causes compatibility problems for some software.

Unless something doesn't work for you after you've tried it out. It's better to just use 64-bit!

you can run 32 bit applications on a 64 bit system with the ia32-libs.

Finding out if you have them from a terminal:

dpkg -l|grep ia32-libs

and for installing type in:

sudo apt-get install ia32-libs

I urge you to use 64-bit.

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Really, compatibility problems? Isn't PAE entirely transparent to userspace? –  poolie Jul 1 '11 at 15:34
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