WPF uses a multilayered architecture:The Managed WPF API -PresentationFramework.dll: holds the top-level WPF types, including those that represent windows, panels, and other types of controls. -PresentationCore.dll: holds base types, such as UIElement and Visual, from which all shapes and controls derive. -WindowsBase.dll: holds even more basic ingredients that have the potential to be reused outside of WPF, such as DispatcherObject and DependencyObject, which introduces the plumbing for dependency properties.The Media Integration Layer -milcore.dll: is the core of the WPF rendering system and the foundation of the Media Integration Layer (MIL). -WindowsCodecs.dll: is a low-level API that provides imaging support (for example, processing, displaying, and scaling bitmaps and JPEGs).Kernel -Direct3D: is the low-level API through which all the graphics in a WPF are rendered. -User32: is used to determine what program gets what real estate. As a result, it's still involved in WPF, but it plays no part in rendering common controls.

http://www.csharptutorial.in/2012/03/wpf-architecture-overview-of-windows.html