Networks are usually designed and build using hardware - routers, switches etc - of a certain type. For example in a company’s network all routers are of type Cisco 3600, the switches are Hewlett Packard 5300, the workstations are Windows XP etc.
Monitor one takes advantage of this fact by using the Class model to group objects that share certain characteristics and provides class-assigned functionality to the individual objects of the same Class. Each individual object is an instance of the Class it belongs to. It is recommended to create a Class for each different type of device.
The SNMP agent of Windows NT4 pretty much differs from the agent implemented in Windows 2000/2003/XP. Therefore, it is preferable to define separate Classes for each OS version.