SQL Server 2005 supports two types of indexes: clustered index and non-clustered index. Here are the main differences between them:

* One table can only have only one clustered index.

* One table can only have many non-clustered index.

* A clustered index requires no separate storage than the table storage. It forces the rows to be stored sorted on the index key.

* A non-clustered index requires separate storage than the table storage to store the index information.

* A table with a clustered index is called clustered table. Its rows are stored in a B-Tree structure sorted.

* A table without any clustered indexes is called non-clustered table. Its rows are stored in heap structure unsorted.

* The default index created as part of the primary key column is a clustered index.