The Devices Model is a representation of the discrete logical units on the system that provide the basic capabilities of the system, such as storage, processing, communication, and input/output functions. There is a strong temptation to identify the system devices with the physical components of the system. This approach is incorrect because what is being managed is not the physical components themselves but rather the operating system's representation of the devices.
The representation provided by the operating system does not have a one-to-one correspondence with the physical components of the system. For example, a modem may correspond to a discrete physical component. It may just as well be provided by a multi-function card that supports a LAN adapter as well as a modem, or the modem may be provided by an ordinary process running on the system. It is very important in using or making extensions to the model to understand this distinction between Logical Devices and Physical Components and not to get them confused.