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Guest D17S

FSX -- OOM -- the 3GB switch -- and VRAM

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I recently bought a new video card (9800Gt 1Gig). I'm working towards building a new system.I've spent time today reading about the 3GB switch and I understand about taking away from the OS and using the USERVA switch to get something between the 2Gig and 3Gig points.I can understand that a video card with more memory (and I'm used to AGP and I understand PCI Express does things differently) will require more of the phyical memory installed on the motherboard for copies or whatever (double buffering???) I'm not a computer guy.what I dont understand is WHERE the video memory is needed. Should I worry about keeping the operating system VAS high or should I worry about letting more go to individual programs? Or is it the case that both the operating system AND the program (FSX) are going to be trying to make 'in system memory' copies of what is going to go to the video card? if its the latter then getting a video card with 1Gig was a mistake.I had intended on using Win XP SP3 with the new system ( a P5Q with 4 Gig of DDr2 and an E8600). I've heard too many bad things about Vista to feel comfortable with it. even the stores are offering free 'downgrades' to XP.Is anyone running a 1Gig video card with XP and 4Gig ram?Can anyone tell me how the video memory affects the VAS (does it deplete the OS side or the user side?) (or both?)Note: I would have put this in the hardware forum but most of the search results I found were in this forum already.

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I only have a 768MB video card (8800GTX) and it works fine with FSX and the three 3GB switch (I have 4GBS RAM on board).You have a little misundertanding of VAS from what I read in your post. The VAS has in the first instance nothing to do with the operating system nor the user application side. VAS is the total address space that can be utilised by a 32bit system 2^^32 = 4GBS. Your video card memory has to be mapped into this address space as well as other ports and bibs & bobs. Your video card takes 1GB of address space so the maximum address space that be used by User applications the operating system and the bibs & bobs is 3GB of VAS. This all means that if you were to have 4GBS of ram onboard only 3GBS could be fitted into the VAS so just over a Gig of your installed RAM becomes unusable. If you only have 2GBS RAM on board about 1.7GBS max would be available to FSX and the rest used by the OS nucleus and any Process requirements. With 4GBS of RAM on board about 2.7GBS would be available to FSX (which is what I get).If this is still unclear then holler I have an analogy That I could write up, that may make it simpler to understand.

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"Is anyone running a 1Gig video card with XP and 4Gig ram?"Not me but I do run 2 (two) 768MB each Nvidia 8800GTX video cards which means they are taking up more than 1 GB of the 4 GB of memory installed. Since I have the Vista OS, I use the USERVA switch and allocate 2560 for FSX. I have not suffered any OOM's with this allocation; however, I will get them if I set my scenery sliders too high. Fortunately, FSX graphics are terrific on my system when the scenery sliders are almost all set at medium levels. If I were building a new system, I would look into the 64 bit OS vs the 32 bit which is restricted to just 4 gigs. I understand most FSXers here on this forum are having little or no problems with the 64 bit. Then you can forget about the 3GB/USERVA switches and add as much RAM (memory) as you want or can afford. A new version of Vista is expected out around the 2d quarter of 2009 and that's suppose to handle memory and performance issues much better so stay tuned....I'm shocked to hear stores are still offering free downgrades to XP. My understanding is that this only applies to users using Vista Business or the Ultimate versions (http://download.microsoft.com/download/5/f/4/5f4c83d3-833e-4f11-8cbd-699b0c164182/royaltyoemreferencesheet.pdf). I heard a lot of people are still having issues with XP too and even with FSX, you still have to apply the 3GB switch on 32 bit systems or else you'll get OOM's. Like politics and religion, this is a sore subject to me so I'll leave it like this. Personally I just can't see why people want to work with old technology and not play with the new and enhance their learning experiences.Good luck on building your new system! Should be fun and educational!Best regards,Jim

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I have had my 8800GTX installed before FSX made its debut. I have been through RTM, SP1 and Acceleration, used no large memory switched then memory switches, I started with 2GB now on 4GB of RAM. I can honestly say that I have never had an OOM message with FSX since I started. I have had the sliders up to the limit of acceptable performance all the way through my FSX experience with as much AI and Autogen as I can get with acceptable performance. I stongly suspect that OOMs have been caused by other factors such as badly managed page files etc.I now have FSX on a Vista64 system as well as an XP SP3 system. Performance appears about the same with FSX on either system. FSX is notoriously difficult to benchmark. I have been using the X3TC rolling demo as a benchmark and Vista64 gives me 5FPS better than XP better using that benchmark unless I use the motherboard onboard sound where they are about the same. I still prefer the XP UI but that is maybe a case of "Better the devil you know than the devil you don't".

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"I stongly suspect that OOMs have been caused by other factors such as badly managed page files etc."Hi John,You ARE right in one respect as badly managed page files can cause an OOM/BSOD/CTD; however, most people, like me, have theirs set to "System Managed Size" (the default). A non-computer expert trying to set up their own page file size is setting themselves up for disaster IMHO. But page files are not the sole cause of OOM's. Even the Microsoft techs admit they have a problem managing large memory allocations, especially in Vista 32bit systems. Even Phil Taylor, formerly the honcho over on the ACES Team (the makers of FSX), stated there was a problem with Vista/XP handling large memory allocations. That's why ACES furnished a patch in the SP2 FSX.exe to allow FSX to use more than 2GB of memory (previous versions of FSX will not allow more than 2GB). That's why Microsoft issued several hotfixes to try to fix problems associated with systems with a lot of memory. These hotfixes have been relatively successful but have not completely solved the problem. That's why Microsoft techs are currently working on an upgrade to Vista to solve memory and performance problems.Best regards,Jim

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Thanks for the responses guys.I think I'm closer to understanding.I've read that a 32 bit OS will only use 3.2Gig of system memory and that confuses things a bit.What I'm hearing though is that my memory cards VRAM must be mapped out of available VAS and then OS and user programs fight over whats left.If I let my video card take 1Gig (3.2 down to 2.2) and then let FSX have 1Gig (2.2 down to 1.2) and let the OS have the remaining 1.2 Gig, that should work just fine right? I could always cut back on the FSX allotment??I read those other therads and I really dont understand why the statement that "FSX only uses contiguous 1M memory blocks" is even there or why it matters.1 meg is pretty small these days. what am I missing?

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Process Explorer tells the story. http://technet.microsoft.com/en-us/sysinte...s/bb896653.aspxhttp://forums.avsim.net/user_files/194489.jpgVirtual Size (VS) causes OOMs at 2G for non-switched 32bit op systems, 3G for switched 32bit op systems and 4G for 64Bit op systems. VS is the op system scheduling ram for future use, NoT physical ram loads. VS can scheduled up to 2-3-4G Per program / process before the op system will OOM (only) That program / process. WS Private is the physical ram load. Notice VS will always lead WS Private. FSX/ SP2 sets the second switch to allow FSX to use VS scheduling above 2Gs and therefore continue to load physical ram until an OOM occurs. Vcard ram forecasts may be part of VS ram scheduling. It would be interesting to see VS with these 1 to 1.5G vcard installs. See what you get.Notice here VS at 2.5Gs and physical ram load at 2G. This is typical for my Vista 64, FSX/SP2/4Gram/9800-512M Vcard setup. My flights would always OOM a 32bit, non-switched system. Here, I'm in that PMDG MD11 out of London on the way to Aerosoft's Franfurt. I'll see over 3G/VS on approach. This would OOM even a switched 32bit system.

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Got lucky on approach.http://forums.avsim.net/user_files/194490.jpghttp://forums.avsim.net/user_files/194491.jpgNote 3G+/VS. This would have OOM'd even a fully switched 32bit op system. We've arrived. 64bit is now necessary for this level of detail. Also notice only ~ 2G of physical ram loaded. Physical ram hit a high of ~ 2.5 mid flight. However after a dinner break pause, is retreated to ~ 2.2G. The pause for this last photo op let it fall off to ~ 2G. http://forums.avsim.net/user_files/194492.jpg

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This discussion seems to overlook the role of the page file and the OS ability to page ram out. Not much good for performance but can effectively extend memory limits.

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True. For ram limited systems (or Any system), set the page file to "system managed. It'll provide whatever function it can. As you describe, page file is about assisting actual, physical ram compensate for inadequate capacity on the stick. VS is an entirely different function. Playing with page file won't cause any change in the VS function and thereby won't help prevent OOMs.

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>I read those other therads and I really dont understand why>the statement that "FSX only uses contiguous 1M memory blocks">is even there or why it matters.The 1Mb contiguous VAS block was a deliberate design decision made by the devs at ACES as one aspect of their efforts towards faster and more efficient address space management.The only reason I mentioned it in my white paper on OOM was to point out why an OOM will occur if there are no 1Mb contiguous blocks available for FSX to use. Even if there were two unallocated blocks of address space available of -say- 950Kb and 260Kb, an OOM would occur because of the 1Mb limit FSX requires.

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I've read that a 32 bit OS will only use 3.2Gig of system memory and that confuses things a bit.
The 3.2GB number is already accounting for addresses lost to video cards etc. As most people are still running video cards with 512MB of video RAM or less, 3.2GB is what is typically left over (ie. 4GB-0.5GB-some other stuff to get ~3.2GB).In your case, it would be more like 4GB - 1GB - some other stuff to get ~2.7GB or so.

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Yea I know, it sure can get that way. The video card does not use the system's physical memory. A 32bit system will recognize (variously) 3-3.5Gs of system physical ram (if installed). Keep in mind this is Physical memory. The Vcard does not use this under Any circumstances. Then . . . there's this other thing called VS (Virtual Size). This is a ram scheduling/forecasting tally sheet the op system keeps in a text file (or the Kernal's version of this). It's only a list or tally sheet. It's not physical ram, Vcard or system. This tally sheet number causes the OOMs. It has nothing to do with the physical memory that is actually being used! It's just a numbers in a "text file." Now, there is some question if VS also includes some projection about the Video card's forecast memory usage too. I really don't know about that. I Do know that VS Always is ~ 500MB Higher than the physical ram load all the time. Is this the Vcard projection? You guys with the 800-1.5G Vcard give it a try. Does VS get Way above the system's physical load? If so, maybe big ram'd Vcards - Will - cause OOMs to occur sooner. I kinda expected these GTX 280/1G Vcards to completely disable FSX. So far it hasn't happened. What's happening!?Science needs you.

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