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We have half a dozen web apps that need to run as 32 bit process but need quite a lot of memory because of various things we're caching, for various reasons this is not easy to change. No one application needs more than 2GB, but the combined memory usages is going to be more than this. For various reasons that are also not easy to change, we're planning to run these all on a pair of 64bit servers with 16GB of RAM, quite enough memory for all the web applications combined memory needs.

Here's my worry. I understand that Windows allocates a virtual address space for each process, 2GB of user space and 2GB of kernel space on Win32 and 8TB of user space and 8TB of kernel space in Win64 (in most cases). The OS then handles which what parts of this address space are mapped to physical RAM. I also understand that the WoW64 subsystem will handle running the 32bit process on a 64bit OS. I don't understand WoW64 well enough to know how it will do this, I would hope that it would map the virtual address space of the different 32bit processes to make use of all the available RAM, but I worry that it may not do this and that the process will still compete for the same set of RAM that has been "ear marked" in some way for 32bit process emulation.

I know the real solution is test our target environment and profile to see what's going on, but a little more information about how physical RAM is managed in under WoW64 would be reassuring.

skaffman
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Robert
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1 Answers1

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There is no "ear marked" 32-bit process RAM. The physical RAM is available to the OS and is given out to processes as needed, whether they are 32-bit or 64-bit. The Wow64 subsystem is not a virtual machine or a process that the 32-bit processes run it. The Wow64 subsystem is a set of shim libraries that handle the 32-bit to 64-bit and vice versa translation.

jcopenha
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  • Thanks, this is what I was hoping to hear. Do you have any links to how the shiming of the OS memory management functions work? – Robert Feb 10 '12 at 15:43