PAE on i686 by default in TH

[Bartosz Świątek]

W dniu 10 lutego 2009 15:59 użytkownik Patryk Zawadzki
<patrys w pld-linux.org> napisał:
> On Tue, Feb 10, 2009 at 3:37 PM, Bartosz Świątek <shadzik w gmail.com> wrote:
>> 2009/2/10 Patryk Zawadzki <patrys w pld-linux.org>:
>>> On Tue, Feb 10, 2009 at 2:23 PM, Patryk Zawadzki <patrys w pld-linux.org> wrote:
>>>> Fedora 11 has declared they only supply an i686 kernel in PAE mode.
>>>> I'd like to propose the same for PLD Th.
>>>>
>>>> Rationale:
>>>>
>>>> * only very old hardware like first Pentium M chips does not support hardware
>> Sorry, can't follow. Only Pentium M does not support Pentium M?
>> Or did you mean that only Pentium M chips do not support EMT64?
>
> Obvious misclick. First Pentium M did not support PAE.
>
>> I have an not too old macbook (>2 years old, macbook 1,1) with an
>> Intel Core Duo that doesn't support EMT64. So an PAE kernel is out of
>> question, not an option for me.
>
> AFAIR EMT64T is needed to run quasi-64-bit code. PAE works by
> remapping memory windows to frames below the 4GB limit while EMT64
> adds longer registers with full addressing. Correct me if I'm wrong as
> I'm no chip expert.

Me neither but I always thought this was one and the same thing.

Here's what wikipedia says:

"x86-64 is a superset of the x86 instruction set architecture. x86-64
processors can run existing 32-bit or 16-bit x86 programs at full
speed, but also support new programs written with a 64-bit address
space and other additional capabilities."

So as far as I understand,  you can use a i686 kernel on your EM64T
(actually I've misspelled it earlier) capable hardware and then enable
PAE (which is a kernel extension, not a hardware one) in order to
address up to 64GB of RAM.

This means, you can not take a 32bit processor (which is not EM64T
capable) and do the same thing.

But again, I can be wrong here.