 The basic premise of the product is to provide an emulation of the lowest layers of the Windows environment in the form of the user.dll, kernel.dll and gdi.dll libraries.As all other Windows dlls depend on these three modules, cloning this functionality allows Windows applications and their associated support dlls to execute correctly on a foreign host system.This approach, as opposed to a full replacement, was thought by the engineering team to be the only rational methodology for success given both the size of Microsoft's ever-expanding efforts and the difficulties of the emulation being precise enough to run commercial grades of software.