What is the difference between ADO and ADO.NET?

ADO uses Recordsets and cursors to access and modify data. Because
of its inherent design, Recordset can impact performance on the
server side by tying up valuable resources. In addition, COM
marshalling – an expensive data conversion process – is needed to
transmit a Recordset. ADO.NET addresses three important needs that
ADO doesn’t address:
1. Providing a comprehensive disconnected data-access model, which
is crucial to the Web environment
2. Providing tight integration with XML, and
3. Providing seamless integration with the .NET Framework (e.g.,
compatibility with the base class library’s type system). From an
ADO.NET implementation perspective, the Recordset object in ADO is
eliminated in the .NET architecture. In its place, ADO.NET has
several dedicated objects led by the DataSet object and including
the DataAdapter, and DataReader objects to perform specific tasks.
In addition, ADO.NET DataSets operate in disconnected state whereas
the ADO RecordSet objects operated in a fully connected state.
In ADO, the in-memory representation of data is the recordset. In
ADO.NET, it is the dataset. A recordset looks like a single table.
If a recordset is to contain data from multiple database tables, it
must use a JOIN query, which assembles the data from the various
database tables into a single result table. In contrast, a dataset
is a collection of one or more tables. The tables within a dataset
are called data tables; specifically, they are DataTable objects. If
a dataset contains data from multiple database tables, it will
typically contain multiple DataTable objects. That is, each
DataTable object typically
corresponds to a single database table or view. In this way, a
dataset can mimic the structure of the underlying database. In ADO
you scan sequentially through the rows of the recordset using the
ADO MoveNext method. In ADO.NET, rows are represented as
collections, so you can loop through a table as you would through
any collection, or access particular rows via ordinal or primary key
index. A cursor is a database element that controls record
navigation, the ability to update data, and the visibility of
changes made to the database by other users. ADO.NET does not have
an inherent cursor object, but instead includes data classes that
provide the functionality of a traditional cursor. For example, the
functionality of a forward-only, read-only cursor is available in
the ADO.NET DataReader object.
There is one significant difference between disconnected processing
in ADO and ADO.NET. In ADO you communicate with the database by
making calls to an OLE DB provider. In ADO.NET you communicate with
the database through a data adapter (an OleDbDataAdapter,
SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter object), which
makes calls to an OLE DB provider or the APIs provided by the
underlying data source.