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Actually, what the OP is referring to is running 32-bit applications in a 64-bit version of Windows. In this case, each 32-bit process cannot use more than 2GB of RAM. The graphics card memory should not be included in the total memory count.
Thus, you can have multiple 32-bit processes running at the same time - and if the physical memory is insufficient to run all of those at once, then they system will begin using virtual memory.
I thought when it came to 32-bit applications they could use up to 4 GB of RAM (like a CPU with 32-bit registers), then part of that 4GB total accessible was mapped to video RAM. I wasn't sure what would happen when you have 4 GB of video RAM let alone primary system memory. How does it handle allocation? If a 32-bit application can only use 2 GB of RAM, then are my 32-bit applications only using 1 GB of primary and 1 GB of video?
It does not work that way. No system process can use any graphics card RAM at all. Thus, only the installed system RAM plus whatever virtual memory space that you have on your system drive(s) should be considered.
So what happens in a 64-bit OS when running a 32-bit app? For instance, if I run Call of Duty 4, how does memory work? The app can never access more than 2 GB of primary system RAM?
Yes. That's basically the case. As a result, with a 64-bit OS and sufficient memory you can play CoD4 while at the same time you are running an anti-virus scan and multiple spyware scans and have multiple Web browser windows open without having to dig into the hard drive's or SSD's virtual memory.
Actually, what the OP is referring to is running 32-bit applications in a 64-bit version of Windows. In this case, each 32-bit process cannot use more than 2GB of RAM.
And how does video RAM play any part in this? How much video RAM is a 32-bit app allowed to use?
I don't think there's an explicit limit to the physical RAM usage, as long as it falls under the virtual memory limit the process is entitled to.And thanks to rflcptr for updating how much virtual memory 32-bit apps can use. I mentioned only physical system RAM in my original determination. 32-bit apps can use up to 2GB of physical RAM and up to 4GB of virtual memory (virtual memory is the combination of physical RAM and the space on a HDD or SSD).
Virtual memory is how the cpu virtualize memory to software (the virtual address space). A virtual address can point to physical memory, the page file or something else.
So with largeaddressaware on, an application can address up to 4GB of physical memory, if that is available.