Dell install Windows 7 Home Premium 64bit on the XPS and include SP1 as well as a few key updates. It is a relatively basic build which is what we like to see.
While being reasonably basic in terms of extras Dell do install numerous useful items at the factory, including Flash and Live Essentials however they also insist on bundling a unwanted extras as well. This includes McAfee and the Bing toolbar which should be left up to the consumer to install, or choose their favoured alternative.
Finally we have the BIOS which on this model uses Phoenix code. There are no performance options present on this system however all of the standard items are available. As with Dells other models BIOS updates are performed in Windows using Dell's flash tool for quick and easy updates.