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I own a Linux workstation which currently has 4 GB of RAM and planning to go for 8 GB in the near future. CPU is a Core2Quad Q9550.

Should I install a 32 or 64 bit variant of Linux?

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You should install 64-bit linux. Even though there are ways for the 32-bit kernel to address more than 4 GB the applications will still have a 3 GB limit.

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  • Thanks for the answer. Are you talking about PAE? Does that work properly in practice?
    – Robert Munteanu
    Jul 15, 2009 at 11:30
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    I am currently using PAE to access 4GB with no problems.
    – Mark
    Jul 15, 2009 at 11:31
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    I'm afraid of PAE. It's like to wake up in 16-bit world.
    – Kirill V. Lyadvinsky
    Jul 15, 2009 at 11:42
  • @jia3ep : any specific reasons to avoid PAE?
    – Robert Munteanu
    Jul 15, 2009 at 12:17
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    Really the only reason not to use PAE is the ~0.1% performance decrease, which is so insignificant that you would never even notice it.
    – Zifre
    Jul 27, 2009 at 14:28
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Here is one overview from LinuxForums.

I would hesitate if you do a lot of work with niche or developing tools written in entirely compiled languages. Many of the projects I'm interested in, like LDC, are only beginning to support 64 bit. Personally I'm holding off, but I'm holding off on more RAM too, so that's not an issue for me.

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    +1 for checking that all the software you need is supported on 64-bit.
    – Mark
    Jul 15, 2009 at 11:32
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32-Bit can only use less than 4 GB for a single process, but it can use more for the whole system. There are not many non-server applications on Linux that will want that much RAM that I can think of.

You will just need to install the PAE (Physical Address Extension) kernel:

sudo sudo apt-get install linux-headers-server linux-image-server

and then reboot. Run top or free and you should more ram. I recommend 32-Bit for desktop users.

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    > I recommend 32-Bit for desktop users. Why? There used to be no 64-bit (Sun) Java plugin and no 64-bit (Adobe) flash plugin, but aren't those two cases solved by now?
    – asjo
    Jul 27, 2009 at 15:23
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You can run a 64-bit kernel and a 32-bit distribution which will give you full access to 4 GB or more of RAM, without the performance penalty of PAE. This is what I do on my machine. Debian has linux-image-amd64 available for i386. Unfortunately Ubuntu doesn't, you'd have to compile your own kernel there, and I don't know if other distributions have packages.

Having said that, for new installations I'd recommend 64-bit as performance is better, so long as you can live with hacks for 32-bit-only binaries like Skype and some browser plugins. RPM distributions have OK support for this at the moment, while Debian and Ubuntu don't, but are working on multi-arch support now, with a first release expected for Ubuntu 9.10 this year.

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    The performance penalty of PAE comes from the extra level in the page table lookup. However, while PAE systems use a three-level page table system, x86-64 systems running in long mode use four levels. If that is the only penalty for using PAE, wouldn't 64bit always have worse performance in this regard? Certainly, 64bit offers some other features which may make up for the tradeoff, but you appear to recommend against PAE due to the extra page table lookup.
    – ChrisInEdmonton
    Jul 23, 2009 at 20:44
  • I have to admit I haven't benchmarked it, and Wikipedia says "On x86-64 processors, PAE is obligatory in native long mode". Ingo benchmarked it groups.google.com/group/linux.kernel/browse_thread/thread/… and 64bit is worse than PAE is worse than 32bit due to page tables in a worst-case fork benchmark. Driver performance will be better if the hardware supports 64bit as bounce buffers won't need to be used, which is the penalty I was thinking of.
    – TRS-80
    Jul 24, 2009 at 3:25
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I'd install a 64-bit version and potentially something like VirtualBox so I can run a 32-bit version in parallel in case I'd need some software that is only available in 32-bit.

You won't be able to make use of more than 4 GB of memory using a 32-bit kernel without jumping through some hoops like PAE which is IMHO better avoided.

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I run 64bit 9.04 for my home desktop. I do quite a lot with this machine, and the only 64bit related issue I encounter is stability problems with 64bit Adobe Flash.

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Go for 64-bit. 32-bit can only access about 3.5 GB of RAM, and most of the compatibility issues have been ironed out. To make it even easier, use a popular distribution like Ubuntu.

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  • My 32-bit Ubuntu is able to use only 2.9Gb. 3.5Gb is a dream :)
    – Kirill V. Lyadvinsky
    Jul 15, 2009 at 11:27
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    My 32-bit Ubuntu is able to use all 12 GB of RAM, though each process is limited. It is not the case that 32-bit OS's can only access about 3.5 GB of RAM. You just have to use PAE, Physical Address Extensions.
    – ChrisInEdmonton
    Jul 23, 2009 at 20:45
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To use all 8 GB naturally you should install 64-bit version.

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