The next version of Microsoft's graphics API DirectX will definitely be different to its predecessors. To be included in the upcoming Windows Vista, DirectX 10 will be the programming interface previously called Windows Graphics Foundation by its developers.
Those people who follow developments in PC graphics hardware will quickly realise that DirectX 10 is designed for the future. Accomodation for graphics 'features' such as Shader Model 4 and higher shows clearly that the programming interface will cater to graphics hardware not even produced yet. But according to news site The Inquirer, at the Games Developers Conference in Europe Microsoft has informed developers that DirectX 10 will 'cut' backwards compatibility with titles written for DirectX 9 and earlier! Those titles will still be able to be run on the system, but will need to run via an additional software 'layer'. It is a fair assumption that titles running via software will operate more slowly.
If this proves to be correct, of course, it will make Windows Vista less appealing than previously to those people who wish to run their existing library of 3D titles on exisiting machines.