The DataReader object helps in retrieving the DATA from a database in a forward-only, read-only mode. The base class for all the DataReader objects is the DbDataReader class.
The DataReader object is returned as a result of calling the ExecuteReader() method of the Command object. The DataReader object enables faster retrieval of data from databases and enhances the performance of .NET applications by providing rapid data access speed. HOWEVER, it is less preferred as compared to the DataAdapter object because the DataReader object needs an Open connection till it completes reading all the rows of the specified table. 
An Open connection to read data from LARGE tables consumes most of the system resources. When multiple client applications simultaneously access a database by using the DataReader object, the performance of data retrieval and other related processes is substantially reduced. In such a case, the database might REFUSE connections to other .NET applications until other clients FREE the resources.

The DataReader object helps in retrieving the data from a database in a forward-only, read-only mode. The base class for all the DataReader objects is the DbDataReader class.
The DataReader object is returned as a result of calling the ExecuteReader() method of the Command object. The DataReader object enables faster retrieval of data from databases and enhances the performance of .NET applications by providing rapid data access speed. However, it is less preferred as compared to the DataAdapter object because the DataReader object needs an Open connection till it completes reading all the rows of the specified table. 
An Open connection to read data from large tables consumes most of the system resources. When multiple client applications simultaneously access a database by using the DataReader object, the performance of data retrieval and other related processes is substantially reduced. In such a case, the database might refuse connections to other .NET applications until other clients free the resources.