Virtualizing a 32 bit guest on a 64 bit os

Question

So I was wondering if anybody knew if there was any performance issues with virtualizing a 32 bit os, in my case 32 bit windows 7, on a 64 bit os, mac osX lion. I remember reading that running 32 bit processes in a 64 bit system can cause performance robbing situations with paging memory. Does this apply to virtualizing or am I misinformed?

I fully understand that the performance of the guest also depends on the amount or memory and cores you devote to your vm, but I was wondering more on the mechanics and the effects of mixing 32 bits with 64 bits.

Thanks everyone.

Solution

in theory it shouldnt be a problem. We could debate the semantics but If you are running any 32 bit programs on your 64 bit computer then you are running those programs in a virtual environment (which you likely are running 32 bit processes). But specifically speaking, when you are running windows on mac, your biggest problems are the challenges that your hypervisor will have in translating windows drivers to interact with the devices on your system. Usually this means the hypervisor works extra hard in keeping everything organized and translated appropriately. Bottom line, your biggest performance drop will have to do with how much power you pull from the processor constantly pegged out. If you are used to 6 hour mac battery life, say hello to 2hr battery life or less.

Comments

[Ben Voigt]

16-bit applications running in the 32-bit VM are going to require emulation when the host has put the processor into 64-bit mode.

[David Schwartz]

You are misinformed. There is no penalty with running 32-bit guests or applications on a 64-bit host OS that isn't more than made up for by the performance benefits of a 64-bit host OS. That is, a 32-bit application or guest will almost always be as fast or faster on a 64-bit host than it would be on an otherwise equivalent 32-bit host.

[Kirill]

I'm running VMWare too and I'm pretty pleased. I was more just wondering if anybody had a better insight to effects of mixing the operatings, if there was any.

[Admin]

That makes a lot of sense. Battery life definitely drops, but that is definitely expected if you making the cpu work harder.

[Rich Remer]

I think that's sort of the crux of the question, isn't it? Does the switch to 32-bit mode and back to 64-bit mode have a performance impact over just running 64-bit all the time.