I've just upgraded to Parallels 8 and has this problem: CPU usage is very high. I use Mountain Lion host with Windows 8 RTM guest. Parallels CPU after starting Windows: 60%-70%, and just stay there non-stop Parallels CPU when running any app: 100%+ (up to 400%) Task Manager in Windows: show very low CPU usage (1%-2%). High usage is shown in OSX's Activity Monitor. My machine is extremely hot when running Parallels. RAM should not be an issue because both the host and guest have plenty (10GB and 6GB respectively).