The new file format (.accdb)

Access 2010 employs a file format that supports a number of product enhancements. When you create a new database, the database uses the new file format by default and is given the .accdb file extension.

You should use the new file format whenever possible because it supports new features, such as multivalued fields and attachments. Moreover, if you want to convert your desktop database to a Web database by using Access Services, the desktop database file must be in .accdb format.

However, the new file format cannot be opened or linked to with earlier versions of Access, it does not support replication, and it does not support user-level security. If you need to use the database with earlier versions of Access, or if you need to use replication or user-level security, you must use an earlier version file format.