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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?

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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
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up vote 23 down vote accepted

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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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
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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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Thanks......... –  Nick.h Dec 30 '10 at 10:23
    
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. –  JUST MY correct OPINION Dec 30 '10 at 14:17
    
thanks for the link! –  Marty Aug 26 '11 at 18:45
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(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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