kernel vs kernel-PAE? why yum install kernel does not install kernel-PAE automatically?

[Kam Leo]

On Sat, Apr 4, 2009 at 6:34 PM, Antonio Olivares
<olivares14031 at yahoo.com> wrote:
>
> Dear fellow Fedora users,
>
> I have a powerful machine with the following specs(smolt profile)
>
> http://www.smolts.org/client/show/pub_7c13bb00-2ebf-42d9-b342-d91f26574bf1
>
> It installed a PAE kernel automatically since it has 3294MB of memory:
>
>        OS: Fedora release 10 (Cambridge)
>        Default run level: 5
>        Language: en_US.UTF-8
>        Platform: i686
>        BogoMIPS: 4810.90
>        CPU Vendor: GenuineIntel
>        CPU Model: Intel(R) Core(TM)2 Quad CPU    Q6600  @ 2.40GHz
>        Number of CPUs: 4
>        CPU Speed: 2394
>        System Memory: 3294
>        System Swap: 5279
>        Vendor: System manufacturer
>        System: P5K Deluxe System Version
>        Form factor: desktop
>        Kernel: 2.6.27.21-170.2.56.fc10.i686
>        SELinux Enabled: True
>        SELinux Policy: targeted
>        SELinux Enforce: Enforcing
>
> It was previously running kernel-PAE-2.6.27.19-170.2.35.fc10.i686, and I decided to update to newer kernel before 2.6.29 comes in, waiting for it :), and I did a
> # yum install kernel kernel-devel kernel-headers
> and I got new kernel, kernel-2.6.27.21-170.2.56.fc10.i686, but it is not PAE.  /boot/grub/grub.conf put this kernel above the other one, but the default=1 instead of default=0.  How do I tell yum to install the PAE kernel automatically or do I have to specify yum install kernel-PAE kernel-PAE-devel kernel-PAE-headers when I update to latest kernel?
>
> What does the PAE kernel offers or does better than the regular kernel?
>
> I tried google, but it does not give me satisfactory answers.  I am sorry to bother with an elementary question, but I want to know what is better for my system.  I also want to know if I get nvidia driver, how does it fare with PAE kernels?, I play a dvd and I see:
>
>
>           ************************************************
>           **** Your system is too SLOW to play this!  ****
>           ************************************************
>
> Possible reasons, problems, workarounds:
> - Most common: broken/buggy _audio_ driver
>  - Try -ao sdl or use the OSS emulation of ALSA.
>  - Experiment with different values for -autosync, 30 is a good start.
> - Slow video output
>  - Try a different -vo driver (-vo help for a list) or try -framedrop!
> - Slow CPU
>  - Don't try to play a big DVD/DivX on a slow CPU! Try some of the lavdopts,
>    e.g. -vfm ffmpeg -lavdopts lowres=1:fast:skiploopfilter=all.
> - Broken file
>  - Try various combinations of -nobps -ni -forceidx -mc 0.
> - Slow media (NFS/SMB mounts, DVD, VCD etc)
>  - Try -cache 8192.
> - Are you using -cache to play a non-interleaved AVI file?
>  - Try -nocache.
> Read DOCS/HTML/en/video.html for tuning/speedup tips.
> If none of this helps you, read DOCS/HTML/en/bugreports.html.
>
> [VO_XV] It seems there is no Xvideo support for your video card available.
> [VO_XV] Run 'xvinfo' to verify its Xv support and read
> [VO_XV] DOCS/HTML/en/video.html#xv!
> [VO_XV] See 'mplayer -vo help' for other (non-xv) video out drivers.
> [VO_XV] Try -vo x11.
>
> .., I have asked for a bit of help and they recommend that I get nvidia driver, I have not used nvidia drivers since Fedora Core 4, but I got good performance back then might help now?
>
> I am sorry to ask too many questions, but many on the list have been very helpful and I appreciate your input :)
>
> Regards,
>
> Antonio

The short answer is you do not need PAE. Your 3GB is within the
address range of the "standard" 32-bit kernel. You need to have 4 GB
or more in order to trigger a requirement for PAE. Link to Wikipedia:
http://en.wikipedia.org/wiki/Physical_Address_Extension