Windows® 2000 Device Driver Book: A Guide for Programmers, Second Edition, The

The Role of Driver Layers in Plug and Play

The WDM model of drivers is built upon structured layers of Physical Device Objects (PDOs) and Functional Device Objects (FDOs). Generally, a PDO exists for each physical piece of hardware attached to a bus and assumes the responsibility for low-level device control common to multiple functions realized by the hardware. An FDO exists for each logical or abstract function presented to higher-level software.

As an example, consider a physical disk drive and driver. It can be represented by a PDO that implements bus adapter functions (e.g., adapting an IDE disk bus to a PCI bus). Once the PDO for the disk bus adapter is realized, an FDO assumes responsibility for the functional operations of the disk itself. ...