Connected data access through the DataReader objects of data provider. This object requires exclusive use of the connection object. It can provide fast and forward-only data access. It doesn't allow editing.
Disconnected data access is achieved through the DataAdapter object. This object establishes connection, executes the command, load data in the DataSet. The dataset works independent of database. It contains data in the memory and can edit the data. The changes in the data can be transmitted to the database using Update method of DataAdapter object.