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Concerns Over No PAE Kernel In Ubuntu 12.04 LTS

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  • #21
    When U drops PAE kernels it increases the work for other distributions which use U kernels (with small mods only). It is certainly correct that mainly the older Pentium M chips are affected, but those are definitely not slower than current Atom cpus. There is basically no need to upgrade those systems when you dont want to do more than surfing the web or writing some letters. But when you can not even install a current distro it is not fun. In the case you use more than 3 gb ram on a system which can handle not user 64 bit but pae you can always install that kernel later, should not be problematic. When you compare the kernel configs the non-pae and pae one those are very similar, so you can derive one from the other. It is definitely no huge problem to maintain two 32 bit kernels. I understand that there is no need for the 64 bit server flavour, i never complied that anyway but there should be a non-pae kernel für 32 bit systems by default. I personally think that most ppl who have got more than 3 gb ram have got already a 64 bit cpu, so in theory you could more easyly drop the pae kernel - that would affect less users...

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    • #22
      ciplogic: PAE is a technology to get 4+ GB of RAM on a system without having to switch to 64-bit.
      Pentium M Dothan CPU's with a 533MHz FSB support PAE very well. The "NX bit" security feature introduced on this revision of Dothan relies on PAE. Pentium M Banias, and Dothans with 400MHz FSB, didn't yet have NX bit so also don't need a proper PAE implementation as much - laptops from that time often still had 512MB of RAM, sometimes even 256, and nobody even cared about having more than 2GB. Many chipsets for laptops also didn't support over 2GB of RAM.

      Isn't there a way to detect if there's a Pentium M CPU and then disable PAE?
      Last edited by AlbertP; 11-10-2011, 09:41 AM.

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      • #23
        When you compile a kernel with pae then there is no way to disable that. Then you need a cpu that has support for this. Similar to a 64 bit kernel that can not run on 32 bit.

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        • #24
          Originally posted by gremble View Post
          PAE kernels do not run on non-PAE machines. Been bitten by this before. This is stated clearly in the article.
          Is this a figment of your imagination? Because I can easily run PAE enabled kernels (Fedora i686 has had them for years) on pre PAE hardware and CPUs.

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          • #25
            Maybe the pae kernel is installed on supported systems when you install it (just like U does). But on a live system it is impossible. It should be easy to verify with vbox without pae. If you have got a cpu that has got no output with

            grep -o pae /proc/cpuinfo

            then you can try it too.

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            • #26
              That is wrong, automatic choosing of PAE/non-PAE kernel also works on live media with syslinux ifcpu64.c32 module.

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              • #27
                Originally posted by birdie View Post
                Is this a figment of your imagination? Because I can easily run PAE enabled kernels (Fedora i686 has had them for years) on pre PAE hardware and CPUs.
                Nope, not a figment at all

                http://sazwqa.wordpress.com/2008/06/...on-virtualbox/

                https://bugs.launchpad.net/ubuntu/+s...ux/+bug/201089

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                • #28
                  Does no one else think the title of the news post is misleading for link clicks?

                  "Concerns Over No PAE Kernel"

                  When the discussion about no non-pae kernel? Not no pae kernel...

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                  • #29
                    @chithanh

                    interesting aspect, but that requires that there EXISTS a kernel, but U wants to drop the kernel completely.

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                    • #30
                      OMG, which idiots running Ubuntu on Pentium II or VIA C3? OMG, ppl are weird ...

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