Windows Aero is a transparent Windows visual style used from Longhorn M6 to Windows 7 (window transparency was removed in 8). The first build to have working Aero is Windows Longhorn build 4039, and the last build to use Aero (with window transparency) is Windows 8 build 8424. In Windows Longhorn, Aero effects relied on the Desktop Composition Engine (or Desktop Window Manager in newer builds), which only worked in a few builds such as 4039, 4066, and 4074. In Windows Vista and 7, it relies on a WDDM driver due to the use of hardware acceleration, otherwise the Windows Basic theme would be used. This requirement was dropped since at least Windows 8 build 7927 with the introduction of a software rendering fallback to the Desktop Window Manager.