Dumb question -- 32 vs 64 bit Windows

[mmganga]

Say I have a 32-bit application which runs (is compatible with) a 64-bit version of Windows (Vista or 7). Can this 32-bit application use more than 4 Gb of RAM (which was the 32-bit limitation of the 32-bit OS)?

Thanks!

 

[Shack70]

I don't think so, the OS will emulate the 32 bit OS to run the app

 

[MagnusTheBrewer]

I think you may be confused. If the program is running on a 64 bit OS then, yes, the application can use more than 4 Gb of ram. The limiting factor is the OS not, the program.

 

[VirtualLarry]

I think you may be confused. If the program is running on a 64 bit OS then, yes, the application can use more than 4 Gb of ram. The limiting factor is the OS not, the program.

32-bit apps can only use 4GB of RAM. Even if the OS supports more.

 

[Nothinman]

Say I have a 32-bit application which runs (is compatible with) a 64-bit version of Windows (Vista or 7). Can this 32-bit application use more than 4 Gb of RAM (which was the 32-bit limitation of the 32-bit OS)?

Thanks!

No and by default it will only get 2G of VM just as if it were running on a 32-bit OS, IIRC. Unless it uses AWE to get around the VM limitations, but that's extremely rare.

I don't think so, the OS will emulate the 32 bit OS to run the app

There's no emulation going on, AMD64 CPUs execute 32-bit code natively even in long mode. Windows does some special things to make sure the right libraries are loaded and such, but that's about it.

 

[ViRGE]

No and by default it will only get 2G of VM just as if it were running on a 32-bit OS, IIRC. Unless it uses AWE to get around the VM limitations, but that's extremely rare.

AWE is only necessary to use more than 4GB on a 32bit application. For more than 2GB, being Large Address Aware (using unsigned INTs for addresses) is enough.

 

[Nothinman]

AWE is only necessary to use more than 4GB on a 32bit application. For more than 2GB, being Large Address Aware (using unsigned INTs for addresses) is enough.

Yes, I understand that...

 

[Anteaus]

On 32-bit Windows systems (XP,Vista,7), any particular program can only use a maximum of 2GB of memory space, even though the OS can support 4GB. This is OS enforced. Most 32-bit software is written with this in mind. This exact reason is why Supreme Commander kept crashing on systems at release. The game would keep trying to write to memory past the 2GB barrier and crash. They later patched the game to only use 2GB and the problems disappeared. This OS implimented limitation can be removed with a switch, but due to stability issues it is turned off by default.

For 32-bit software running under 64-bit (Vista,7), this cap was increased to 3GB. So in practice 32-bit software has up to 3GB available, however since most 32-bit software was written with the 2GB limit in mind you'll find most programs will simply keep themselves under 2GB by design.

 

[her209]

The application doesn't know nor does it need how much physical RAM is installed. It addresses memory using virtual memory addresses which the OS, Windows in the instance, handles the conversion from virtual memory addresses to physical addresses. That's the theory anyway.

 

[Nothinman]

The application doesn't know nor does it need how much physical RAM is installed. It addresses memory using virtual memory addresses which the OS, Windows in the instance, handles the conversion from virtual memory addresses to physical addresses. That's the theory anyway.

It's not theory, it's how it VM works and why you get a SEGV if you try to access memory outside of your current VM range. But applications can indeed query how much physical memory is in the system, how much VM they have access to, etc and change their usage patterns accordingly.