32bit OS cannot see 4GB of RAM on modern chipset

[J de Boyne Pollard]

MSS> I have a machine built on Intel G33 chipset (Asus P5K-V mobo).
MSS> 64bit OS (2003 R2 SP2 Ent) sees all 4GB of really present
RAM.
MSS> 32bit OS (XP SP2 Pro) sees only 3.24GB of RAM, with PAE on.
MSS> Why is this?

Read <URL:http://dansdata.com./askdan00015.htm>.

MSS> Any chances of fixing this by tuning some OS registry
MSS> settings or the BIOS settings?

No.

[Maxim S. Shatskih]

> Read <URL:http://dansdata.com./askdan00015.htm>.

Can Microsoft people confirm or deny this cite from the above URL:

"For this reason, Microsoft changed the behaviour of the /PAE option in all
versions of WinXP as of Service Pack 2. They fixed the endless driver problems
by, essentially, making /PAE in XP not do anything. All versions of WinXP
except for the x64 Edition now have a hard 4Gb addressing limit, no matter what
hardware you use them on and what configuration you choose."

Is this true? Well, PAE is definitely on, since Data Execution Protection
requires PAE (no NX bit in pre-PAE PTEs), and is on even on 1GB Acer laptop.

But what about the memory addresses? are they really truncated by the OS to
32bit even in PAE mode? what about Server 2003 32bit? is it suffering from the
same artificial limitation?

If it is so - is there any Windows setting to switch this off and use 36bit PAE
physical addresses? I expect only the miswritten and buggy drivers have PAE
issues, and, since I have no PCI cards in the machine, I expect the out-of-the
box MS's drivers to be fine with 36bit physical addresses.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
ma...@storagecraft.com
http://www.storagecraft.com

[Herman D. Knoble]

On Mon, 05 Nov 2007 06:30:25 -0800, J de Boyne Pollard <j.deboyn...@tesco.net> wrote:

-|MSS> I have a machine built on Intel G33 chipset (Asus P5K-V mobo).
-|MSS> 64bit OS (2003 R2 SP2 Ent) sees all 4GB of really present
-|RAM.
-|MSS> 32bit OS (XP SP2 Pro) sees only 3.24GB of RAM, with PAE on.
-|MSS> Why is this?
-|
-|Read <URL:http://dansdata.com./askdan00015.htm>.
-|
-|MSS> Any chances of fixing this by tuning some OS registry
-|MSS> settings or the BIOS settings?
-|
-|No.
I'm running an Intel Pentium 4, and XP Home Edition with all available Windows Updates.
This is a Dell Optiplex GX620 with 4 GB RAM. The system Icon shows that a little less
than a half GB is used for various caches (like ATI adapters). The Task Manager shows:
Total Physical Mememory = 3668036 K or 3.66 GB.
Commit Charge = 374M/5469M.

So what do you mean by "see"?

Skip

[Maxim S. Shatskih]

> Total Physical Mememory = 3668036 K or 3.66 GB.
> Commit Charge = 374M/5469M.
>
> So what do you mean by "see"?

Total Physical Memory is _significantly_ smaller then 4GB.

[Peter Wieland [MSFT]]

True. On 32-bit client versions of the OS you're limited to physical
addresses < 4GB even with /PAE turned on. /PAE still gets you NX
compatibility but won't let you see those last few MB. It's a policy
decision that included some marketing decisions as well as the expectation
that too many existing PCI drivers were going to fall over when faced with a
36-bit address.

-p

--
This posting is provided "AS IS" with no warranties, and confers no rights.

"Maxim S. Shatskih" <ma...@storagecraft.com> wrote in message
news:OafDC18H...@TK2MSFTNGP02.phx.gbl...

[Maxim S. Shatskih]

> True. On 32-bit client versions of the OS you're limited to physical
> addresses < 4GB even with /PAE turned on. /PAE still gets you NX
> compatibility but won't let you see those last few MB. It's a policy
> decision that included some marketing decisions as well as the expectation
> that too many existing PCI drivers were going to fall over when faced with a
> 36-bit address.

Thanks Peter!

Am I correct that 32bit Server 2003 is free from this limitation?

[Peter Wieland [MSFT]]

Yes it should be.

--
This posting is provided "AS IS" with no warranties, and confers no rights.

"Maxim S. Shatskih" <ma...@storagecraft.com> wrote in message

news:ORl6tjF...@TK2MSFTNGP04.phx.gbl...