Data Access in VB

DAO,RDO and ADO are connection objects that use OBDC to connect from program to data.

DAO = Microsoft? Data Access Objects (DAO)
ADO = ActiveX Data Objects (ADO) data connection
'There are a wide variety of ODBC drivers you can use with ADO totalk to data. In the future, there will be more OLE DB providers available to connect to data stores. The Microsoft? OLE DB Provider for ODBC is currently the default provider for ADO. You can use a different
provider by setting the Provider property of the Connection object'.

RDO = 'Remote Data Objects (RDO) is specifically designed to access remote ODBC relational data sources, and makes it easier to use ODBC without complex application code. RDO is a primary means of accessing SQL Server, Oracle, or any relational database that is exposed with an ODBC driver'.
The words in quotes are extracts from MSDN articles which give examples of using each. A good place to start is :-
http://msdn.microsoft.com/library/default.asp?url=/nhp/Default.asp?contentid=28001860&gssnb=1

DAO - helps to link the database directly without creating ODBC
RDO & ADO - helps to link the database with help of creating ODBC
Diff: We have to use ODBC in RDO & ADO but not needed in DAO.