jenslyn wrote...
Just look at what processes uses the CPU.
I assume you see your CPU usage in the task manager, and the task manager also allows you to view how much CPU the individual processes uses. That way you know why your PC is idling at 50%.
One process which often use the cpu allot is the indexing service which enables you to search your files faster, and since vista/win7 claims to be "better" at this, then this service must also run longer or more often.
Another common CPU/IO hog is the Superfetch service, more so on Vista than on 7. What Superfetch does is caches applications that you use more often so the load faster when you open them. It can be disabled in Computer Managment under the Services menu and it will show up in the Task Manager as "svchost.exe."