What is 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. PAE is supported on the majority of computers today and it is an easy procedure to enable it in Ubuntu, if it is not already. To check if your processor supports PAE, try:

grep --color=always -i PAE /proc/cpuinfo

In general, a proper 64 bit system is recommended if you have 4 Gb or more memory and/or want to get the full benefit of the 64 bit architecture (see 32bit_and_64bit), but in some cases making a complete switch to 64 bit is not desirable, and using PAE can be a viable compromise.

It should be noted that there is no "Virtual Address Extension." i.e. The applications still get the same amount of virtual memory since the virtual addresses are still 32 bits while the physical addresses are 36 bits. Therefore PAE is not at all equivalent to a 64 bit system.

Forcing PAE support on Pentium M processors

Many Pentium M processors have PAE support, but do not announce it by default. Starting with 14.04, the user can manually force to add the PAE flag to the processor information, enabling the use of these processors with newer Ubuntu versions.

Instructions on installing and upgrading these systems can be found at PAE/PentiumM.

Enabling the PAE kernel on older releases

Starting with Ubuntu 12.10, the generic default kernel already has PAE support enabled. For more information, please see the 12.10 alpha 1 technical overview, and the announcement by the Ubuntu Technical Board.

For older releases, refer to PAE/Enabling.