Windows Seems Slow

If Windows performance seems slow, try the following:

Quit applications and programs you aren't using: If you run a number of memory-consuming applications and programs simultaneously, Windows performance may become slow. Quit any applications that you aren't using. You can also use Activity Monitor (located in the Mac OS X Finder in Applications > Utilities) to see how much of your Mac's memory each application is using. That way, you'll have a better idea of which applications cause performance to degrade the most.
Change how much memory is allocated to Windows: Parallels Desktop is set to allocate a certain amount of your Mac's available RAM memory to Windows and the rest to Mac OS X. If too much memory is allocated to Windows, Mac OS X may slow down, which in turn can cause Windows programs to slow down because they're running on top of Mac OS X. If, on the other hand, too much memory is allocated to Mac OS X, then Mac OS X applications may run well but Windows programs might slow down.
To optimize the performance of both Windows and Mac OS X, set the memory allocated to Windows to be somewhere within the recommended range, indicated by the graphic under the memory slider in the CPU & Memory configuration panel.
Antivirus software may slow down your virtual machine: Windows may become slower after you install antivirus software. To be protected, you have to sacrifice performance.
Note: Do not install more than one Windows antivirus program.
Run fewer virtual machines at once: If you are running multiple operating systems at once using Parallels Desktop, stop one or more of them to improve performance of the others.
Run Windows locally: If you start Windows stored on an external storage device connected to your Mac (for example, an external USB disk drive), its performance will be lower than if it were stored on your Mac.
Tune Windows for speed: To speed up Windows, select Tune Windows for speed in the Optimization pane .
Disable log messages: If you select Use detailed log messages in the Advanced pane of Parallels Desktop Preferences, Parallels Desktop will start creating a more detailed log file. It can be helpful for the Parallels support team, but uses more hard disk space and may slightly lower the system performance.