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| '''PAE, Physical Address Extension''' | = What is PAE? = |
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| [[http://en.wikipedia.org/wiki/Physical_Address_Extension|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 }}} |
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| '''2013-5-2: The page is in writing. Please don't edit now ''' | 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 [[https://help.ubuntu.com/community/32bit_and_64bit|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. |
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| 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. | |
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| = Forcing PAE support on Pentium M processors = | |
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| A guide for getting computers with older Pentium M processors to work with the latest Lubuntu. | 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. |
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| '''Instructions on installing and upgrading these systems can be found at [[PAE/PentiumM]].''' | |
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| = Enabling the PAE kernel on older releases = | |
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| '''Starting with Ubuntu 12.10, the generic default kernel already has PAE support enabled.''' For more information, please see the [[https://wiki.ubuntu.com/QuantalQuetzal/TechnicalOverview/Alpha1#Linux_kernel_3.4|12.10 alpha 1 technical overview]], and the [[https://lists.ubuntu.com/archives/ubuntu-devel/2012-May/035176.html|announcement]] by the Ubuntu Technical Board. | |
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Physical Address Extension (PAE) is a feature found on almost all 32 bit processors produced after Pentium Pro, that is younger than around 1995. Because PAE is close to being ubiquitous it is now a requirement for Buntu: During installation the processor is prompted for the PAE flag, and only if present the process will carry on. Up to and including 12.04 Buntu offered a PAE and a non-PAE release, but from 12.10 only the PAE release is maintained. A number of older Pentium M processors produced around 2002-5 (the ones with 400 MHz front side bus) do not display the PAE flag, and hence a standard installation fails. However, these processors are in fact able to run the latest (and hence PAE-demanding) kernels if only the installation process is modified a little. In spite of their age many of the affected computers (IBM Thinkpads, for example) are suitable for today's use if given a light distro like Xubuntu or Lubuntu; among other advantages they have a low power consumption. This guide describes a workaround for installing the latest Lubuntu and bringing them back to life. The process might take some time but is not difficult. Everybody can manage, and if you are unfamiliar with giving commands at the command line, fear not! Just write the commands exactly as they appear here, keeping in mind that upper- and lowercase are different. Before proceeding: If the installation is failing, are you sure the problem is related to PAE? A lot of misunderstandings flourish, and lack of PAE support is often blamed as the reason for a failed installation when in fact As a first step please try installing a regular 13.04 Xubuntu or Lubuntu ISO (including the alternate Lubuntu). Only if you get the error ”” this guide comes into play. ---- Now we know that the problem is in fact related to the PAE flag. This gives several options: * Install Xubuntu 12.04, which is supported through april 2015. Lubuntu 12.04 is only supported through october 2013. * Install the 12.04 non-PAE kernel and follow a certain upgrade path. * Install a modified Lubuntu 13.04 which supports non-PAE processors. * Use another distro like Puppy Retro. The guide is focusing on option 2: We are going to add a fake PAE flag to the output of cpuinfo, and after that we are able to upgrade to 12.10 and 13.04. The idea comes from a thread posted by 7bit. An upgrade is always a risky process, and in general a fresh install is preferred. In order to minimise the risk of something going wrong we keep the installation as small as possible during upgrade. Only when the system has reached the latest version the full selection of packages is applied. |
For older releases, refer to [[PAE/Enabling]]. |
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.