Re: Downloading and naming

[Stephen Powell <zlinuxman@fastmail.com>]

On Mon, Aug 1, 2016, at 19:30, Pascal Hambourg wrote:
> Le 01/08/2016 à 04:02, Stephen Powell a écrit :
>>
>> To the best of my knowledge, there are no 32-bit-only processors which
>> support the NX bit.  A 32-bit PAE-enabled kernel can only use NX if it
>> is running on a 64-bit-capable processor.
> 
> You should check your information. A number of late 32-bit Pentium 4 and 
> Pentium M models support the NX bit.
> 

Perhaps there are some 32-bit-only processors which support XD/NX.
But none of mine do.
>>
>> To give a specific example, my IBM ThinkPad X31 has
>> a Pentium M processor, which is PAE capable and 32 bit only  (...)
>> And the PAE kernel
>> can't exploit the NX bit, because the processor doesn't support it.
> 
> This is really surprising because, according to 
> <https://en.wikipedia.org/wiki/Pentium_M>, Pentium M models which 
> support PAE also support the NX bit. Actually, PAE support was added 
> just to support the NX bit, the physical address size is still 32 bits.
> 

You should check your information.  :-)
That same Wikipedia article that you quoted above also says this:

"The Banias family processors internally support PAE but do not show the
PAE support flag in their CPUID information ..."

All Pentium M processors support PAE, they just don't all advertise such
support in the output of the CPUID instruction.  My IBM ThinkPad X31 has
a Banias-class Pentium M processor.  I can get a PAE-enabled kernel to run
on it, but I must use the "forcepae" kernel boot parameter in order to get
it to work.

My original point remains.  If one's computer has less than 4 GiB of
memory installed, and the processor does not support the XD/NX bit, then
running a 32-bit PAE-enabled kernel does not benefit one at all.  In
fact, it actually hurts one, because a PAE-enabled kernel uses more
memory.

Debian is one of the few distributions to still provide non-PAE kernels.
And I applaud them for doing so for just such situations as I described
above.  Just because one's processor supports PAE doesn't necessarily mean
that one benefits from using a PAE kernel.  In addition to my IBM ThinkPad
X31, I have two other 32-bit-only machines.  One uses a Pentium 4 processor,
the other uses a Xeon.  None of them support the NX bit.  And none of them
have more than 4 GiB of memory installed.  (Only the ThinkPad requires the
"forcepae" kernel boot parameter to get a PAE-enabled kernel to run.)

-- 
  .''`.     Stephen Powell    <zlinuxman@fastmail.com>
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