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From: Paul on 21 Jan 2010 11:59
Peter Olcott wrote:
> "philo" <philo(a)privacy.net> wrote in message
> news:auGdnf_g6tqmpMXWnZ2dnUVZ_upi4p2d(a)ntd.net...
>> Peter Olcott wrote:
>>> Why would less than the full 4.0 GB show up on the
>>> control panel->System dialogbox?
>>
>>
>> Without PAE a 32 bit OS can only address about 3.2 gigs of
>> memory
>>
>> if you need 4 gigs or more...you will need to use a 64bit
>> OS
>
> It says that it has Physical Address Extension on the same
> screen that says that it has 3.24 GB of RAM.
>

PAE is capable of addressing more than 4GB on a 32 bit OS,
but Microsoft doesn't want you to have it :-)

http://en.wikipedia.org/wiki/Physical_Address_Extension

"Windows XP Service Pack 2 and later, by default, on processors with the
no-execute (NX) or execute-disable (XD) feature, runs in PAE mode in order
to allow NX.[11] The "no execute" (NX, or XD for "execution disable") bit
resides in bit 63 of the page table entry and, without PAE, page table entries
on 32-bit systems have only 32 bits; therefore PAE mode is required if the NX
feature is to be exploited.

However, "client" versions of 32-bit Windows (Windows XP, Windows Vista,
Windows 7) limit physical address space to the first 4 GB for driver
compatibility [12] and licensing[13] reasons, even though these versions
do run in PAE mode if NX support is enabled."

And this article does an experiment to remove the bounds and address more
memory. An interesting read...

http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm

Paul

From: Jon Danniken on 21 Jan 2010 13:03
Paul wrote:
>
> PAE is capable of addressing more than 4GB on a 32 bit OS,
> but Microsoft doesn't want you to have it :-)
>
> http://en.wikipedia.org/wiki/Physical_Address_Extension
>
> "Windows XP Service Pack 2 and later, by default, on processors
> with the no-execute (NX) or execute-disable (XD) feature, runs in
> PAE mode in order to allow NX.[11] The "no execute" (NX, or XD for
> "execution disable") bit resides in bit 63 of the page table entry
> and, without PAE, page table entries on 32-bit systems have only
> 32 bits; therefore PAE mode is required if the NX feature is to be
> exploited.
> However, "client" versions of 32-bit Windows (Windows XP, Windows
> Vista, Windows 7) limit physical address space to the first 4 GB
> for driver compatibility [12] and licensing[13] reasons, even
> though these versions do run in PAE mode if NX support is enabled."
>
> And this article does an experiment to remove the bounds and address
> more memory. An interesting read...
>
> http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm
>
> Paul

Wow, that is a very interesting article. Thanks for posting it!

Jon


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