I've had, and finally fixed, a problem where Win 8 running in Parallels uses a lot of CPU on my Mac -- even when I'm not doing anything. That makes the Mac hot, the fan loud, and the battery-life short. So, it's a bad thing. If you suspect this is happening to you too, you can see the cause more directly by running "Activity Monitor" on the Mac, and clicking the CPU column to sort results by CPU use. If you have this problem, Parallels will be at the top with near-100% CPU usage even when Win 8 isn't doing anything.
I see on the web that many people have this problem. http://forum.parallels.com/showthread.php?262881-Parallels-8-high-CPU-when-idle-MBP-2012-10-8-1
As the link above shows, no one quite understands the problem, but they CAN tell one key thing: the problem goes away if you do certain seemingly-irrelevant things. Here's what I did that fixed it for me: I opened a Command Prompt window, typed "services.msc" and pressed Enter. This popped open the Services dialog box. I scrolled through looking for Windows Media Player, as one comment in the link above recommends. There was no problem with the Windows Media Player setting, so I closed the Services dialog box. Voila! I didn't change anything, yet Parallels is no longer running the Mac CPU so much. Other people got the same effect by logging out of Windows and then back in.
It feels a bit like waving four-leaf clovers rather than science, but it works! So, I hope this note helps anyone else experiencing this problem!
Thanks for the tip, Steve!
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