A MIB is a collection of MOs. It defines the following attributes of an MO:
Object name
Access authority
Data type of the object
The Structure of Management Information (SMI) stipulates how to define and organize the MOs. It also defines the data types for these objects, for example, Counter and Gauge.
The MIB designates the variables maintained by the network elements. The variables are the information that can be queried and set by NMS. The MIB provides a data structure of the combination of the all the possibly managed objects on a network.