When Parallels first started supporting Vista, it would max out one CPU at nearly 100%, even when the virtual machine was essentially idle. With each release candidate, Parallels has improved greatly, and the CPU usage has dropped to about 40% on my (1st-generation) MacBook Pro. Posting in the Parallels Forum, feuerri has found a simple way to reduce this even further:
I just discovered that by changing the Start -> Control Panel -> Power Options in Vista Enterprise (running under build 3150), I was able to reduce the CPU consumption from 37-40% to about 17-20%.
It works for me, and a number of other people have reported success. No word on whether there’s a noticeable slowdown with this setting, but there are a few settings you can experiment with and see how it works for you. Link
- Parallels Desktop for Mac Forum — Link