Hi Everyone: I currently have 4 GB of Ram. I am thinking of upgrading to 8 GB. Some programs will not use more than a certain amount even if you have it present. Question: If I get 8GB of RAM, will FSX even bother to use it, or is there a cap on how much RAM FSX is capable of using regardless of how much you purchase? Thanks, Chris

FSX is a 32-bit application and can'tuse more than than 4Gb of Virtual Address Space and hence RAM.

However, if you add another 4GB you will have 4GB dedicated that FSX can utilize without the OS / other apps pinching some off you.

FSX is a 32-bit application and can'tuse more than than 4Gb of Virtual Address Space and hence RAM.

OK - can you help me? I'm a a bit confused - if FSX is a 32 bit application, than why does PMDG recommend running a 64 bit OS for their 737NGX? I upgraded to Windows 7 last week for this purpose. Does this make no difference now after all this?

I don't know, but my hypothesis is due to the fact that the ngx runs mostly outside of fsx. In there introduction I think it mentions something like think of ngx running outside of fsx or like a stand alone app and using fsx to display the world and allows the user to interact with it.

OK - can you help me? I'm a a bit confused - if FSX is a 32 bit application, than why does PMDG recommend running a 64 bit OS for their 737NGX? I upgraded to Windows 7 last week for this purpose. Does this make no difference now after all this?

I suggest that it's because a 64-bit operating system offers 4Gb whereas 32-bit can only offer about 3Gb even with the /3GB switch. It's been reported in other threads that running FSX on a 64-bit system reduces (if not eliminates) OOM errors.

I suggest that it's because a 64-bit operating system offers 4Gb whereas 32-bit can only offer about 3Gb even with the /3GB switch. It's been reported in other threads that running FSX on a 64-bit system reduces (if not eliminates) OOM errors.

Correct. In fact, without modifying the default settings 32-bit Windows will only allow applications to use up to 2GB of address space. Also with 32-bit Windows, there is no benefit from installing more than 4GB of physical memory. On a typical installation only around 3GB of physical memory is actually usable, the rest is masked by video memory and various system devices. On 64-bit Windows, the main benefit from having more than 4GB is that you avoid reading memory pages from the harddrive, even with other applictions running besides FSX (Google Earth, flight planners, weather utilities, whatever else you run).

if FSX is a 32 bit application, than why does PMDG recommend running a 64 bit OS for their 737NGX?

Because under a 64 bit OS, *each* 32 bit application can use up to 4GB (of course, you need to have more than 4GB, because the OS itself needs memory), but on a 32 bit OS, no more than 4GB can be allocated in *total*, counting the OS, the apps, and including the RAM dedicated for the video card and other expansion boards so, the memory available for FSX under a 32 bit OS it's usually than 3GB, and becomes less and less, the more RAM you have on the video card (this means a 2GB video card used with 32 bit OS is a big no-no). A flight sim airplane or utility, if it's made with .GAUs and/or .DLLs (most of the addon airplanes are), run in-process with FSX, so it shares the same pool of 4GB max that FSX can use on a 64 bit OS. If it's made as an .EXE file, even if it's launched alongside FSX, it can allocate its own pool of memory, up to 4GB.

Well they have said all that needs to be said. Go win 7 64 bit.

Firstly fsx is a 32 bit and a 32 bit system is limited to 3 GB , a 64 bit system can handle memory above 3 gb, but FSX would not use more than 2 GB. So go ahead with win 7 and put in 4 GB.

Firstly fsx is a 32 bit and a 32 bit system is limited to 3 GB , a 64 bit system can handle memory above 3 gb, but FSX would not use more than 2 GB. So go ahead with win 7 and put in 4 GB.

FSX SP2/Acceleration can use 4 Gb of VAS on a 64-bit system because it has IMAGE_FILE_LARGE_ADDRESS_AWARE set

FSX SP2/Acceleration can use 4 Gb of VAS on a 64-bit system because it has IMAGE_FILE_LARGE_ADDRESS_AWARE set

Oh is that so, then I should also install Acceleration. I currently only have sp1 and sp2 .

What on earth could you do in FSX to use more than 2 GB ram? Seriously. I've only reached the upper 1's on a few occasions (with the exception of errors). With a PMDG aircraft running, UT2, ASE, REX, and a bunch of addon scenery, I don't even get close to 2.

It's about allowing room for other applications outside of FSX, including the OS itself, to stretch out. Having more than 4GB on a 64bit OS, even when running 32bit apps is a very good thing. Additionally, 64bit OS's tend to manage memory allocation more efficiently as well.

To go a little further to explain the numbers, a 32-bit OS can only access 2^32 bytes, which comes out to the 4Gig max RAM value. Without some sneaky hacks, that is the limit of RAM that you can use. But the top 1Gig of that 4Gig range is reserved for system use, such as I/O registers and video card mapping. That is why if you have 4 gig of physical RAM in a motherboard, the OS will only recognize 3Gig of it, since the top 1Gig is reserved. All 32-bit programs (such as FSX, IE, Office, etc....) also can only use 3Gig RAM. Without the /3gig switch, actually each 32-bit program can only use 2Gig of RAM. Only programs compiled with the /3gig option have access to 3Gig of RAM. EDIT: Looks like I was a bit wrong. In a 64-bit OS, 32-bit programs can use 4Gig RAM with the /3gig switch set. In a 32-bit OS, they can only use 3Gig. Learn something new everyday! But a 64-bit OS can access 2^64 bytes, which is a really large number I can't remember :) . But at the top of that range, there is a reserved section for I/O and Video memory, it is just that we cannot stack enough RAM to hit that limit. So if you put in 4 or 8gig of physical RAM, a 64-bit OS will see all of it, and can use it. And that is why a 64-bit OS is so great, since with an 8gig RAM system, you can have two 32-bit programs running in Windows, each with a full 3Gig of physical RAM allocated to it, and still have 2gig of RAM for the OS itself, without having to swap to disk or anything. Note that this is from memory, and for x86 CPU's running Windows. Server OS's can use PAE (sneaky hack) to access more RAM, and I think OSX and Linux can, but I don't know much about them. But for running XP or Win7, this is pretty accurate.