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Does anyone have any information on performance between Windows 2008 32bit and 64bit guests running on a VMware ESXi 4.1 host? We're interested in what a default OS install should be - assuming there is no other restriction.

Say for example the guests for comparison are 4GB RAM and 2 vCPU configs running Windows Server 2008 Std with the same disk sizes on the same shared storage. (PAE mode enabled on the 32 bit machine to support extra RAM.)

I'm assuming that the differences are negligible, but open to people's experiences.

Edit - OK the 4GB scenario seems too logical to use 64bit. What if the comparison guests were only 2GB of RAM?

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If you're running 4Gb of RAM you should be using 64-bit regardless, otherwise you're throwing away 512Mb of RAM. PAE has its own overheads, and you can still only access a 2 (or 3Gb) application memory space, and you can still only access 3.5Gb of RAM at a time, the "window" just moves. –  Mark Henderson Jul 21 '11 at 4:02
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up vote 1 down vote accepted

We have a lot of hosts with about 25% of our guests being Windows, I would have to say I have no reason to believe that ESXi handles a 64-bit client any better or worse than a 32-bit one. Regardless of this being a VM I think it's time to say good-bye to the 32-bit world and I would urge you to do the same.

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There is an interesting discussion on the VMware community site. My own subjective experience is that 64 bit is a little faster. Since that is the natural growth path I think new installations should just be 64 bit by default.

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Thanks Keith, had seen that one but it's a little old and didn't have any definitive data. I suspect that hasn't changed and the differences all lead to the main decision point of RAM allocation. –  Mike Jul 21 '11 at 4:48
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