Virtual PC™ and Virtual Server™ machines support virtual machine additions, or virtual machine extensions, that add features to a virtual machine and its operating system. These additions can improve the compatibility between the host operating system and the virtual machine's operating system and can make the two work together better. Some virtual machine additions improve the graphics, mouse control and time synchronization of a virtual machine and include additional features for file transfers and sharing. Depending on the operating system the virtual machine uses, additions can be optional features or come default with the operating system.
When one first installs an operating system in a virtual machine, there may be performance issues stemming from the virtual machine's default configuration. Virtual PC™ can support various operating system versions, so it configures graphics settings it believes to work best with the guest operating system. Although one can adjust the amount of memory, central processing unit (CPU) cores and disk space a virtual machine utilizes, the virtual machine's performance still may not be as desired. In addition, switching between the virtual machine and the host computer may require more work than it could if using virtual machine extensions.
Virtual machine additions improve performance by adding optimized graphics drivers, improving mouse cursor tracking and improving time synchronizatfion. After one installs the additions, he or she will likely have access to higher resolutions and color settings that result in overall better graphics. Extensions also improve how the mouse cursor works and make it easier to click on areas both inside and outside the virtual environment. If extensions aren't installed, the user will have to use a key combination to switch between the virtual machine's window and the guest operating system. Time synchronization is an optional feature but makes sure the virtual machine's time is the same as the host machine's.
Another useful feature of virtual machine additions is that they enable easy file transfers between the virtual machine and its host. They allow one to drag and drop files to and from the virtual machine and also support the use of shared folders. If virtual machine additions are not installed, users will be limited to files within the virtual machine's operating system and any computers in its virtual network. Shared folders appear on the virtual machine's desktop and are as easy to access as its own hard drive's folders.