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Windows Driver Model

The Windows Driver Model (WDM) - also known (somewhat misleadingly) at one point as the Win32 Driver Model - is a framework for device drivers that was introduced with Windows 98 and Windows 2000 to replace VxD, which was used on older versions of Windows such as Windows 95 and Windows 3.1, as well as the Windows NT Driver Model.

WDM drivers are layered in a complex hierarchy and communicate with each other via I/O request packets (IRPs). The Microsoft Windows Driver Model defined a unified driver model for the Windows 98 and Windows 2000 lines by standardizing requirements and reducing the amount of code that needed to be written.

WDM drivers will not run on operating systems earlier than Windows 98 or Windows 2000, such as Windows 95, Windows NT 4.0 and Windows 3.1. By conforming to WDM, drivers can be binary compatible and source compatible across Windows 98, Windows 98 Second Edition, Windows Me, Windows 2000, Windows XP, Windows Server 2003 and Windows Vista (for backwards compatibility) on x86-based computers.

WDM drivers are designed to be forward-compatible so that a WDM driver can run on a version of Windows newer than what the driver was initially written for, but doing that would mean that the driver cannot take advantage of any new features introduced with the new version.

WDM is generally not backward-compatible, that is, a WDM driver is not guaranteed to run on any older version of Windows. For example, Windows XP can use a driver written for Windows 2000 but will not make use of any of the new WDM features that were introduced in Windows XP. However, a driver written for Windows XP may or may not load on Windows 2000.