ReactOS Driver Model
The ReactOS Driver Model is the ReactOS equivalent of the Windows Driver Model; the Windows Driver Model was a replacement for the VXD model used before Windows 98, and the NT Driver Model used before windows 2000.
Device drivers are hardware specific extensions to the ReactOS Executive. They allow the Operating System to interact with certain devices and visa versa. ReactOS currently aims to implement the NT driver mode, of which the Windows Driver Model (WDM) is a subset of. WDM is a set of rules for writing portable Windows drivers. The Windows Driver Foundation (WDF) introduced in Windows Vista is also a consideration for future development.
There is a difference between NT3, NT4 WDM in one hand and 2000/XP WDM drivers in the other hand. The old OSes use the IRP method that originated in DEC's VMS. Later it was decided that IRP was to much complicated so a new way was devised that was called fastIRP. In fact it was a complete U-turn toward the Unix way to communicate between kernel and drivers: IRP are asynchronous and not so predictable and it was not easy to use in stacks of drivers like what is common now with anti virus or HID. This change happens at the same time in NT and OpenVMS.