I'm running Ubuntu 10.04 and want to run Windows 7 in a virtual machine. I have a 64-bit system so I can run 64-bit Windows, but I'm wondering if this is a good idea or not for a virtual machine. Will it be faster? Will it use more resources and slow down the host oS?
I think that other factors, such as the hard drive arrangement you are using, will have a much greater impact on performance.
A 64-bit guest OS is unlikely to slow down the host OS any more or less than a 32-bit guest, unless you allocate more memory or CPU cores to the virtual machine. However, if you install a 64-bit guest you at least have the option for the guest OS to address more than ~4GB of memory; depending on the application (and your hardware), this could improve performance.
I see you have an answer in 2010. For 2012, the same question remains. I'd say, if you have 4 GB or less of real ram (i.e. host machine), use Windows 7 32 bit. If you more than 4GB of host RAM, use 64 bit Windows 7.
Why? I used a 32bit Windows 7 VM for development on a mac because my old Macbook (2GHz Core2Duo, 4GB RAM) would choke on the 64bit version (slightly larger memory footprint - for me just over the tipping point). On my 16GB Macbook Pro Retina, the same VM runs ridiculously fast but sometimes chokes when pushed (SQL Server 2012 + Visual Studio 2012 + Azure emulators + 25 browser tabs etc) since it sees only 3.5GB of it's 8GB virtual RAM. Given there is no upgrade path from 32bit to 64bit and that we're in 2012 (better CPU, RAM etc) err on the side of 64bit versions. Now ... I've to reinstall Win7 64bit in my VM ...
Ok, so I was super curious myself and run numbers after I reinstalled Windows 7. Here are some actual benchmark numbers for us!
Test is: to measure time taken to compile a Visual Studio 2012 solution
Outcome: Appears that in this specific task, 64bit (and access to more ram) helps by 10%.