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?

  • 2
    Note that PAE requires hardware support. If you install the pae kernel on hardware that doesn't support it, your system may crash. Install the generic kernel in such situations.
    – apoorv020
    Dec 30 '10 at 10:29

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.

  • Thanks, and why last time I installed ubuntu it was pae and now it's generic?
    – Nick.h
    Dec 30 '10 at 10:23
  • @EliahKagan ty for this - this post was way before 11.04 and was later extended to 11.04 and 12.04 but not for 11.10 - fixed
    – Takkat
    Jul 23 '12 at 19:53
  • 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.
  • 1
    PAE kernels give you SOME of the features of 64-bit systems. Like larger amounts of addressable RAM. You're still only using 32-bit processing in 32-bit mode, PAE or no PAE. Dec 30 '10 at 14:17

(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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.