3GB switch in XP

[Wildblue 244]

Hi,I have 3GB memory. I tried the 3GB switch together with the setting to make fsx ready to handle more than 2GB. Didn't work out for me. Fsx starved out, to less memory available for the pci-e graphics card i think, i got 0.5 fps and the scenery was all white, no textures. I can sort of understand this with the 512 Mb video card i have.ButTo my knowledge there is no such thing as a 2.5GB switch. Yet in a silly mood i changed the 3GB switch to 2.5GB in the bios.ini. And this worked reasonably well for me in a 30 minutes flight.Yet, when i set this to 2.3GB it's all wrong again, the same symptoms as with 3GB.I don't understand for the life of me. When a 2.5GB or 2.3 GB switch does not exists how can i have different results between those two???And i don't use this with userva.

[AWACS 12]

I have 3 GB of memory yet, windows xp doesn't seem to recognize it, can you tell me the switch you are talking about so I can get all 3 GB running?Thanks,Jeff

[GHD 21]

I stuck in another couple of 1GB sticks the other day and didn't use the /3GB switch. All of the memory is recognised:Now 4GB is another kettle of fish ;-)George

[PhilTaylor 45]

This is all about control of the OS and the app wrt virtual address space. You have to mod both, and understand what mod is doing what.The /3G switch for the OS mods the OS default behavior at boot, and tells the VMM ( virtual memory manager ) to allow the app up to 3G of process address space, if the app is so marked, instead of the default 2G. So that mod tweaks the OS.Then you have to mod the App. Marking FSX with 2560 tells the VMM to only let it allocate up to 2.5 of the 3 it could potentially get it. I suggest that to give the OS more headroom; since 3072 with a 768M 8800 leaves the OS 256MAs far as why 2560 seemed to work better than 3072 for the OS boot, I'd have to go ask the kernel guys, that sort of fine-grained knowledge is not at the tip of my tongue.

[PhilTaylor 45]

The /3G switch isnt about recognizing the memory, thats all together a different story. The /3G switch is about enabling the OS and the App to use a different mapping for process address space. By default the potential 4G process address space for a 32-bit app is split in 2, with 2G virtual address space for the App ( the lower 2G ) and 2G virtual address space for the OS.The /3G switch enables the OS to grant more space to the App. The App has to be marked to take advantage.This is all "virtual memory". I cover this in a bit more detail on my blog.Getting physical memory recogized is a dance between the mobo, the chipset, firmware ( BIOS ) and the OS. And then the VMM has more physical memory to map the virtual process address space to. Which is a good thing.And yes getting 4G recognized is hard because then you are dependent on certain mobos with chipsets and even certain BIOS revs within a chipset. It can be very hard to get that last G recognized.

[Guest mz-cd]

Hi all, I have this with interest.I installed 3gb of ram a long time ago but know nothing about this "switch".So after installing the ram have done nothing.Where can I read more about it and how to allocate the memory.Many thanksRegardsRichard

[jordanal 70]

After a bit of searching before implementing the /3GB swith on my WinXP unit, I saw plenty of Vista examples of the "IncreaseUserVA" switch for Vista, but no eqqivilent for XP. I found the MS articles for XP, mentioning the "userva" switch. I then successfully flew the LDS-767 without an OOM error last night with 2560 set. This was with only 2GB of Physical RAM and a 640MB GPU.I added the "/3GB /userva=2560" switches to my boot.ini file like so:(boot loader) << should be bracketstimeout=0default=multi(0)disk(0)rdisk(0)partition(1)WINDOWS(operating systems) << should be bracketsmulti(0)disk(0)rdisk(0)partition(1)WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptIn /3GB /userva=2560Good Mirosoft Articles for WinXP boot.ini:Available boot.ini switches:http://support.microsoft.com/kb/833721How to properly edit your boot.ini file in WinXPhttp://support.microsoft.com/kb/289022/How to use the "userva" swith in WinXP:http://support.microsoft.com/kb/316739/