PAE on i686 by default in TH

[Bartosz Świątek]

2009/2/10 Bartosz Świątek <shadzik w gmail.com>:
> 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.
>

And I now think I am :)

Again wikipedia:

"Physical Address Extension (PAE) is a feature of x86 and x86-64
processors that enable the use of more than 4 gigabytes[1] of physical
memory to be used in 32-bit systems, given appropriate operating
system support. PAE is provided by Intel Pentium Pro and above CPUs
(including all later Pentium-series processors except the 400 MHz bus
versions of the Pentium M), as well as by some compatible processors
such as the Athlon and later models from AMD."

So it's definitely just a software extension, which means 32bit
processors will support it too.

Ok, I'm fine with it if you decide to enable PAE by default.