Allocation

• Virtual PC 2007 tasks users with allocating specific amounts of hard disk space and RAM, or Random Access Memory, to the guest operating system. Since the resources allocated are not available for the host system while the guest is running, allowing a guest to use larger amounts of the system's resources can adversely affect the host's ability to run Virtual PC 2007 and other applications.
  
  

Guest Performance

• Conversely, guest operating systems require enough resources to run correctly, and allocating more memory and space allows them to complete tasks more efficiently. Though a guest operating system will run faster with additional resources, robbing the host of necessary memory slows overall system performance.
  
  

Balance

• Overall system performance while running Virtual PC 2007 is a balance between the host and guest systems. Ideally, the guest system should be allocated enough RAM to operate within its recommended system requirements, while leaving the host enough to run its basic functions without undo effort.