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I have an iMac with the quad core i7 CPU which shows up in Mac OS X as an eight core CPU (thanks to Hyper Threading, I think). Parallels Desktop allows me to assign 1-8 cores to the Windows VM that I'm running. How would changing that number affect the Host OS performance? Currently I have 2 cores assigned to the VM, but it is unclear how Parallels manages them. Are those the real cores or the virtual cores? I always see only 4 cores being used in Mac OS X, the remaining 4 (I guess those are the virtual ones) never show any activity.

For example - can I assign all 8 cores to the VM and still use Mac OS X? Say I'd like this for gaming (w/o going to Boot Camp), etc.

Or if I assign 3 cores, 5 cores - real processors always have either 1 or some even number of cores.

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