Windows Layered Driver Architecture
1. application
The application handles requests from users and other applications, and calls either the Win32 API or a routine that is exposed by the user-mode client driver.
2. A user-mode client driver
handles requests from applications or from the Win32 API. For requests that require kernel-mode services, the user-mode client driver calls the Win32 API, which calls the appropriate kernel-mode client or support routine to carry out the request. User-mode client drivers are usually implemented as dynamic-link libraries (DLL). Printers support many operations that can be performed in user mode, and so typically have user-mode clients; disks and other storage devices, networks, and input devices do not.
3. A kernel-mode client driver
handles requests similar to those handled by the user-mode client, except that these requests are carried out in kernel mode, rather than in user mode.
4. A device class and miniclass driver pair
provides the bulk of the device-specific support. The class driver supplies system-required but hardware-independent support for a particular class of device. Class drivers are typically supplied by Microsoft.
A miniclass driver handles operations for a specific type of device of a particular class. For example, the battery class driver supports common operations for any battery, while a miniclass driver for a vendor’s UPS device handles details unique to that particular device. Miniclass drivers are typically supplied by hardware vendors.
5. A corresponding port driver
(for some devices, this is a host controller or host adapter driver) supports required I/O operations on an underlying port, hub, or other physical device through which the device attaches. Whether any such drivers are present depends on the type of device and the bus to which it eventually connects.
All driver stacks for storage devices have a port driver. For example, the SCSI port driver provides support for I/O over the SCSI bus.
For USB devices, a hub and host controller driver pair perform the duties of the port driver. These drivers handle I/O between the devices on the USB bus and the bus itself.
A corresponding miniport driver handles device-specific operations for the port driver. For most types of devices, the port driver is supplied with the operating system, and the miniport driver is supplied by the device vendor.
6. At the bottom of the figure is the hardware bus driver.
Microsoft supplies bus drivers for all the major buses as part of the operating system. You should not attempt to replace these drivers.