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Nick.h
Asked: 2010-12-31 01:57:57 +0800 CST

What's the meaning of "-pae" at the end of kernel version?

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Last time I installed Ubuntu there was a "-pae" at the end of the kernel version in the boot screen. Now that I've reinstalled Ubuntu from the same disk instead of "-pae" there is a "-generic" at the end of kernel version.

What's the meaning of those terms? Why do they different between two installations?

kernel pae

3 Answers

  1. Best Answer

    PAE stands for P-hysical A-ddress E-xtension to access 4 GiB RAM on 32-bit systems. This is not needed for a 64-bit Ubuntu.

    for 11.10 and earlier

    For 32-bit Ubuntu a PAE kernel is automatically downloaded and installed on a system with more than 3 GB of RAM. Otherwise, and if no network connection is available the generic kernel is used.

    for 12.04 LTS

    Note that from Ubuntu and Kubuntu 12.04 LTS a PAE kernel only can be installed from the 32-bit installation CD. This may cause problems on old hardware when the CPU does not support PAE.Release Notes

    In this rare cases we may have to install 32-bit Lubuntu or Xubuntu that still come with a non-PAE-kernel. We can install the Unity desktop later. Alternatively we may also install 32-bit 10.04 or 11.10 with the non-PAE kernel first. With an upgrade to 12.04 a non-PAE-kernel can also be upgraded to a non-PAE-kernel.

    Ubuntu 12.04 LTS is the last release to support a non-PAE kernel.

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    • Thats PAE - Physical Address Extension is a technology which allows 32 bit operating systems to use up to 64 Gb of memory (RAM), something which is normally achieved by switching to a 64 bit system.
    • To know more details about PAE look at this link.
    • PAE kernels give you the feature of 64 bit systems (the ability to use >3.2gb of RAM)
    • Where the generic kernel with 32 bit cant.
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  3. (PAE) stand for Physical Address Extension. It's a feature of x86 and x86-64 processors that allows more than 4 Gigabytes of physical memory to be used in 32-bit systems.

    Without PAE kernel, you should see something as follows:

    free -m

    Sample output:

    enter image description here

    To enable PAE, open terminal and type the following command:

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

    Reboot your machine.

    Now check again :

    free -m

    Sample output:

    enter image description here

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