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Thread: difference between default and "pae" kernels

  1. #1

    Default difference between default and "pae" kernels

    Hello,
    After some software installation acrobatics, I came to the situation where my open SUSE 11.1 boot menu displays (among other things) a "default" kernel and a "pae" kernel. Can someone, please, provide a short explanation, or provide a reference to an explanation of what that means?
    Regards,
    bostjanv

  2. #2

    Default Re: difference between default and "pae" kernels


  3. #3
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    Default Re: difference between default and "pae" kernels

    Offhand I don't remember all the details (IIRC explained somewhere in a wiki or newsletter article), but the primary reason for making the -pae version the default is not actually the -pae memory addressing function. In fact, the default kernel supports larger memory addressing without pae. But there are other tweaks in the -pae kernel considered beneficial - possibly the NX flag, a cpu security enhancement that protects against buffer overflows - and that is why it is the default.

  4. #4
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    Default Re: difference between default and "pae" kernels

    I use the PAE Kernel so I can use my 4GB RAM. 64-bit Version of openSUSE doesn't work too good on this system at the moment.

  5. #5
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    Default Re: difference between default and "pae" kernels

    This is one of those topics on which there is a lot of confusion and at least what appears to be contradictions. The 32-bit linux kernel is actually capable of supporting the hardware extensions which enable up to 64GB of RAM; this is done with a technique known as "highmem". However, given memory mapping considerations, the practical limit is 16GB. PAE (36-bit addressing) is AFAIK not the method by which this was implemented in the kernel, and hence a PAE kernel is not required for >4GB addressable memory. But the "pae kernel" does implement other features, which is why it is used by default. Note that highmem is a compilation option; it is not found in all distro kernels.

  6. #6

    Default Re: difference between default and "pae" kernels

    Thanks for the replies. Regards, bostjanv

  7. #7
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    Default Re: difference between default and "pae" kernels

    Guys,

    Just need a lil bit more info..

    I installed my suse11.1 today, after adding some softwares from the cd i restarted it and it came up with 4 options .. default and pae other two were for debug default and pae..

    Now when i open default it doesn't take me to X Windows but leave me on command prompt.

    But when i start from PAE it just work fine..

    Intel 2.16 Dual Core
    4GB Ram
    Laptop.

    Should i be worry about anything.

    I do not have any problem in the performance yet

  8. #8
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    Default Re: difference between default and "pae" kernels

    I forgot to mention i am using 32bit.. not 64

  9. #9
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    Default Re: difference between default and "pae" kernels

    and you're using a proprietary driver for your videocard? Then you installed it on the pae kernel. So when you boot the default kernel your xorg.conf is configured to use the proprietary driver, which is there for the pae kernel, but not for the default. In your case this is OK, since you need the pae kernel to get full usage of your 4 GB RAM.
    - Athlon X6 3.6 GHz, 16 GB DDR3, 64 GB SSD, 3 TB of disks, GT540, openSUSE Factory + KDE
    - ASUS A73SD, Intel + GT610M Optimus, 6 GB, 2 x 120 GB SSD, openSUSE Factory + KDE

    Anything that can go wrong.... will teach us

    http://en.opensuse.org/User:Knurpht
    http://nl.opensuse.org/Gebruiker:Knurpht

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