Athlon 64: Can 32bit app on 64bit OS address >4GB?

[fbg1]

I understand that the upcoming x86-64 version of Windows will be able to run both legacy x86 apps and new 64bit apps (can the x86-64 Linux distros do this too?). Does anyone know if the 32bit apps will be able to address >4GB of system memory? Is that dependent on the app, or the OS?

 

[Saem]

If you have 32bit addressing, you cannot address more than 4 gigabytes.

 

[Crusher]

The OS should handle all requests for memory, the app just asks the OS for however much it wants. The 4GB limit has nothing to do with the operating system. The problem is that 32-bit processors aren't capable of addressing more than 4GB of RAM. Windows 2000 Advanced Server supports 8 GB of RAM, but it has to be running on a computer that has Intel's Physical Address Extension. Windows 2000 Datacenter supports 64 MB of RAM in specialized hardware configurations.

 

[Colourless]

Memory segmentation theortically allows x86-32 to address upto 64 GB of memory (48 bit FAR pointers), BUT it will only work with very specific processors with operating system and application support.

If x86-64 is designed so the memory address translation is always done in 64 bits, then yes, theoretically, it would be possible to use upto 64 GB of memory with x86-32 apps. I would actually imagine this is what they actually do. However the operating system will need to have the memory managment code written in x86-64 to setup the page tables and segment descriptors, otherwise you'll still be limited to 4 GB max.

 

[fbg1]

Thanks all. So it depends on whether MS codes that ability into Windows 64 or not. Makes sense. Any Linux users know how x86-64 Linux does it (Suse, I think)?