When do I need the PAE Kernel?

I have a 64 bit machine with 4 Gb RAM and presumably no need for the PAE Kernel.

But I have a 32 bit machine also with 4GB RASM. Should I have the PAE kernel in that, or is it only needed for RAM > 4GB (or what, I’m hazy about the PAE Kernel).

Some machines see it, some don’t I would try the desktop, but during an
install it should work out which one. You can always install both :wink:

Cheers Malcolm °¿° (Linux Counter #276890)
SUSE Linux Enterprise Desktop 11 (x86_64) Kernel
up 2 days 4:14, 2 users, load average: 0.11, 0.13, 0.18
GPU GeForce 8600 GTS Silent - CUDA Driver Version: 195.36.15

I’m fairly certain kernel-desktop will see the RAM in most cases. But as M said, the installer will usually get it right.

PAE stands for physical address extension, you need it to address more than 4GB
of physical RAM with a 32 bit processor, as mentioned above the installer should have already made this decision.

When in YaST, be sure to click the “details” tab and verify the installer finds the amount of RAM installed, also a good idea to run the pre install memory test routine provided you have the time.

On my hardware ( Athlon 64 x2 Qt-64 @ 2.1Ghz and 4 GB of Ram ) 1 full pass was about 2 hours and 3 min. it is a very thorough test, took a bit over 26 hours to run 13 passes.

Regards, Cfn7

“Patience is virtue” Confucius

True, but it does more than just extend the access to RAM. On a 32bit machine is simulates some 64bit functionality using only 32bit processing. Is it really needed if you don’t have 4GB + memory unsure. My Laptop under 11.1 default install didn’t use PAE first time and ran fine. After an unintentional mistake and re-install, the default used PAE and ran 2 to 5% faster with still only 2GB RAM.

Very informative, thank you all for that.

I wonder if the opposition have any PAE-like code for 32 bit machines in their distros, or maybe in their latest, window 7, anyone know?

Most distros do PAE

Windows…‘cough - cough’:stuck_out_tongue: Don’t make me laugh!

caf4926 wrote:
> Windows…‘cough - cough’:stuck_out_tongue: Don’t make me laugh!

i ran a full 32 bit desktop for years (OS/2) before Redmond released
their first consumer grade (aka: almost reasonably priced)…

and, first ran 64 in 2005…

DenverD (Linux Counter 282315)
CAVEAT: http://is.gd/bpoMD
posted via NNTP w/TBird | KDE 3.5.7 | openSUSE 10.3 SMP i686
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At the possible expense of taking your question more literally than you would like:

no, no need, but…

I’m not sure that there is ever a need for a PAE kernel, but, in some circumstances it may be desirable.

On my laptop (1 G ram) and 11.1 I was surprised (and gratified) the installer automagically decided that the PAE kernel was appropriate and installed that for me without any intervention on my part. I was expecting to have to do that myself, so I was really, really happy to find that out (not that its a big issue, but it just gives you a 'warm ‘n fuzzy’ to have someone get it right without you having to intervene).

PAE is commonly packaged with NX (no execute) and this gives an appreciable extra degree of protection against buffer overflow attacks. This, as much as anything was why I was keen on a PAE kernel.

The non-PAE 32 bit kernel can only map 4G of memory, and, in practice, you get to see a bit less than that. But at, say, 2G or less, there is no need for PAE in order to see the full amount of memory, but NX may still be very desirable.

Above 4G of memory, the PAE kernel can be used and can make available a memory space of 4G per process. For most people that could be an advantage, but you can come up with corner cases (one very big process and not much else) in which it doesn’t really deliver much.

For most recent x86-compatible processors, the technical possibility exists of running 64 bit software. Firstly don’t think that this will cause it to run twice as quickly; it won’t. Some things will run a bit more quickly, some will run a bit more slowly and the balance will probably be a slight, but not a big, advantage, except for special cases. Secondly, some memory structures are a bit bloated in 64 bit, so it is probably undesirable to run 64 bit on low memory systems, even if you have the option.


The non-PAE 32 bit kernel can only map 4G of memory
I thought it was nothing over 3GB

Very interesting, on my box (32 bit 1GB Ram) when 11.0 was installed GRUB had a PAE option which of course I had to try, I must admit it did seem a bit faster and as M observed the buffer overflow attack vulnerability is certainly logical.

I still do quite a bit of Windoze support, I don’t enjoy it but on disability every bit helps, on really bad cases where preservation and recovery is imperative the box running ClamAV, Avast for Linux, and Sleuth Kit is the platform I use for virus scan, removal and recovery, think I’ll try the PAE option on the next one.

One thing you have to say for “Micro-Squish”, as long as folks buy it techs will always have supplemental income, although is at the pain and suffering of the unenlightened masses.

DenverD has posted his Linux counter registration and I think thats an outstanding idea, I encourage all that have not registered to do so, it’s anonymous quick and easy, the more of us there are the greater the incentive to port apps. http://counter.li.org

Regards, Cfn7 (Linux counter 485948)

box running ClamAV, Avast for Linux, and Sleuth Kit is the platform I use for virus scan, removal and recovery
You don’t think that might be a bit of overkill?:slight_smile:
BTW: my fl. zip 34652;)

With the Intel architecture in 32 bit mode any process can only map 3 gig since the top 1 gig of addresses are reserved for the OS. PAE is basically bank switching so for address above 4 gig the address space is bank switched. This is a relatively slow process so for large memory models this can slow things down. Also any given process will not see more then 3 gig. Normally this is not a problem.

Hi caf4926,
The box uses clam/fresh klam mostly for email, it plays nice with the version of Thunderbird I have and no one could believe the trash my degenerate friends send (as if one couldn’t imagine what a degenerate I am)

When a really infected, scrambled drive is encountered it gets plugged into the “fugly box” and gets scanned by clam, then avast which is only a manual scanner on Linux, scanning a drive with a utility that is not native is quite a bit faster and more thorough. The combination will find things even MBAM, Root killer and combi fix miss running as a native utility.

Sleuth Kit ( GUI for Autopsy ) is just a good forensic toolkit, am I an expert? NO WAY, but I can get around and recover most if not all data in oh say 8 out of 10 cases, not as good as I want but my clients are usually happy with the outcome.

Anyway overkill, possibly but in reality there just tools, a mechanic can't have too many tools, like too much fun or too much money or in my case, Chicago born kid turned Jazz loving Florida redneck after 60 years, too many guns, is it possible?

My Zip, 33549, Lutz ( Pronounced “Lootz” locally )

Some info on pae, first from https://features.opensuse.org/305694, note this quote (post#17):

Regarding the PAE vs. non-PAE kernel: We will install PAE kernel only if the PAE flag is present && (machine has >3GB RAM or NX flag is present), which will avoid the performance hit caused by PAE on machines where it has no use.
and post#9 here from a couple of years back: openSUSE Forums - View Single Post - kernel pae…what’s new?