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Whether you have seen it on the Web or in the brief introduction, Windows Vista has a new look and feel. Unlike the last few versions, the change is not skin deep. The changes to the graphical interface go much further. Actually, the changes go straight to the core. Previous versions of Windows used the graphical device interface (GDI) as its primary application programming interface (API) for handling various 2D output devices. While GDI formed the basis for 2D and most of a user's interface experience, DirectDraw and Direct3D were created for 3D games and applications. Starting with Windows 2000, device drivers were required to conform to the Windows Driver Models WDM. That is all kernel-mode device drivers needed to meet a standard. Each new version made earlier version features of WDM available in the new version unless there was need for a major change. Below you can see the Windows XP driver model (XPDM) and its interaction with other APIs and their runtimes.
All previous versions of Windows used a 2D interface. Users of Vista now can choose to utilize a 3D desktop. Due to the rise in power that can be delivered in modern graphics cards, Microsoft has taken a totally different approach creating the Windows Vista Display Driver Model (WDDM).
Under the former regime, it was not uncommon for the system to crash if the graphics subsystem crashed. This is not the case with Vista. From Windows NT to XP the driver model was part of the kernel. This change was to facilitate faster graphics performance but cost system stability since a faulty driver could take down what kernel pioneer Per Brinch Hansen called the "system nucleus." At the kernel mode, a process can overwrite memory that belongs to another process or practically anything else it wishes.
This has had its hazards and Microsoft did something about it because modern graphics processors have become as complex, if not more so, than CPUs. This complexity demands the attention of robust drivers such as the 34.6 MB Catalyst 6.12 driver for Windows XP download on AMD/ATI's Website. Moving parts of the drivers out to the user space (WDDM User) alleviates detrimental crashes from bad drivers. A kernel-mode driver (KMD) operates where it needs to but the main portion of the driver stays outside the precious core. Graphics is not the only area getting this new arrangement as it happened for USB, printer, audio and others. This movement of the driver to the user space allows for something not seen before: the possibility that you can install a new driver and NOT have to reboot.