3.25GB out of 4.0GB on 32-bit OSes on D975XBX2

[mickrussom]

The long and short of it:

64 bit Linux sees all 4GB.

64 bit Windows sees all 4GB.

An Opteron 280 system with a Tyan S2892 sees all 4GB in 32 bit windows.

However, this board only sees 3.25GB in 32 bit mode on Vista, Windows 2003 and XP. I've tried PAE mode, tried everything in the "boot.ini" (BCDEdit.ex) to get this to stop.

Has anyone ever gotten to the bottom as to why a motherboard needs 768MB of "reserved PCI configuration space"?

[vddobrev]

This is a very good article on the subject: http://www.dansdata.com/askdan00015.htm
In summary, a 32bit OS can only address 4GB total, includind reserved memory for devices like video cards and what not, i.e. the 768MB you listed.

[IRQ Conflict]

Thats right. It's a limitation of winXP 32bit. Thats why I run a max of 3GB's. 1024/ 512 /1024 /512.

[Sparky]

IRQ Conflict , do you see a noticeable performance increase in apps (photoshop for example) using 3gb vs. 2gb?

I too tried 4gb and had the same problems, went back to 2gb's.

[IRQ Conflict]

Can't say for sure as I went from 1GB to Three. I already had two 512's when I built the system, then added two gigs when the modules went on sale. I've never done any testing with just the two gigabytes. But I of course noticed a marked improvement overall with the three.

The amount of video ram has an effect on overall system ram being used I believe. Don't quote me on this but I think if you have a video card with 512- 1GB of GDDR, that counts as system ram as well so going over two gigs with one of those may be a waste. I'd have to look into it. I can't remember where I heard that though.

I'm currently running two 256MB X1950 Pro's in Crossfire. Windows XP Pro recognizes the three gigabytes and increased the page file to 3069MB's. But it is strange that it says the recommended page file size is 4063MB's

[old stuff]

Here is a MS KB article on the memory limitation on 32bit Vista: http://support.microsoft.com/kb/929605

[mickrussom]

Here is a MS KB article on the memory limitation on 32bit Vista: http://support.microsoft.com/kb/929605

I've read this. As I've indicated, I got an opteron dual core 280 system on a Tyan S2892 that takes 4GB and shows 4GB on 32 bit windows, so I consider this a non-answer from Microsoft. I believe it has to do with the PCI configuration space and there is something Intel could do about this.

I'm happy with 3.25GB out of 4.0 (better than 2.0, 2.75, etc), but I get rather sore when I see the opteron machine do it just fine with no PAE or other special configuration, but our Intel 975XBX2 doesn't do it an no one from Intel is offering a good reason as to why.

Did you read the article, by the way, the stupid thing basically says run 64 bit windows. I don't know about you, but my statement on 64 bit windows is "it doesn't run anything", it runs all 32 bit on WOW64, makes strange placements of DLLs in system32/system/system64, damages a bunch of subsystems, lots of legacy apps choke, I've been on 64 bit windows since "windows xp 64 bit aka windows 2003 sp1" , vista 64 bit and windows 2003 64 bit, great as a server OS, impractical given the huge amount of legacy stuff that chokes for a desktop.

[vddobrev]

Here is a MS KB article on the memory limitation on 32bit Vista: http://support.microsoft.com/kb/929605

I've read this. As I've indicated, I got an opteron dual core 280 system on a Tyan S2892 that takes 4GB and shows 4GB on 32 bit windows...

Can you mention which 32bit Windows? 2000? 2003?

[mickrussom]

Can you mention which 32bit Windows? 2000? 2003?

Windows 2003 with SP2 integrated. I could also try Windows XP 64-bit if it is claimed that this is a "desktop" board.

Also, the same problem happens with Vista 32-bit, which I run daily.

[DJL]

Here is a MS KB article on the memory limitation on 32bit Vista: http://support.microsoft.com/kb/929605

I've read this. As I've indicated, I got an opteron dual core 280 system on a Tyan S2892 that takes 4GB and shows 4GB on 32 bit windows, so I consider this a non-answer from Microsoft. I believe it has to do with the PCI configuration space and there is something Intel could do about this..

There is nothing Intel can do about it - its a limitation of 32bit systems. I'd be very, very surprised if your opteron system actually has 4GB available in a 32bit system. Where is that being reported?

What graphics card to you have in the XBX2 system?

I'm happy with 3.25GB out of 4.0 (better than 2.0, 2.75, etc), but I get rather sore when I see the opteron machine do it just fine with no PAE or other special configuration, but our Intel 975XBX2 doesn't do it an no one from Intel is offering a good reason as to why.

The PAE switch doesn't do anything in most desktop versions of Windows now - not that it will help with your problem.

Bottom line - If you want all your 4GB install a 64bit OS.

[mickrussom]

There is nothing Intel can do about it - its a limitation of 32bit systems. I'd be very, very surprised if your opteron system actually has 4GB available in a 32bit system. Where is that being reported?

What graphics card to you have in the XBX2 system?

The PAE switch doesn't do anything in most desktop versions of Windows now - not that it will help with your problem.

Bottom line - If you want all your 4GB install a 64bit OS.

Intel could address the matter technically. "Install 64 bit windows" doesnt cut it.

The TYAN S2892 was reporting that total memory in task manager as 4GB with 1MB being 1048576 bytes.

The card is the 8800 GTX.

Funny, PAE works in Linux to access 4GB (and more). Seems to be an interesting problem involving how memory / configuration space is laid out. Some machines go as low as 2.75GB , some 3.25, others dont seem to have the problem at all (In my own experience w/ the Opteron).

I'd like to see more technical references as to why PAE wouldnt work (not that I would want that - but that should work and does work w/ Linux 32-bit ) or a concrete explanation as to how 768MB of memory can't be seen, yet there is a working page file (So the total available pool of memory is larger than 4GB).

And again, to all those who extoll the use of 64-bit windows, its really very hacky and not really ready for primetime use except as a server. As a desktop its rife with issues.

Also, lets then forget the "Desktop OSes", I said the problem will happen with Windows 2003 SP2 Enterprise Ed., thats not a desktop OS.

I have, in the past, routinely seen more than 4GB on Windows with PAE. It doesnt allow a given process to see more than 4GB, but it certainly increases the pool of available memory beyond 4GB.

Since I have exactly 4GB in this box, I really cant tell if PAE is even being turned on or not.