Data Dictionary Views Vs Dynamic Performance Views

Oracle 10g contains two types of metadata views:

• Data Dictionary Views (Ex: DBA_TABLES, DBA_USERS, DBA_VIEWS)
  
• Dynamic Performance Views (Ex: V$DATBASE, V$VERSION)
  

Data dictionary views have names that begin with DBA_, ALL_, and USER_

DBA_TABLES: All tables in the entire database reserved for user accounts that have DBA privileges
DBA_USERS: Shows information about all the users in the database
DBA_VIEWS: Shows information about all the views in the database
ALL_TABLES: All tables owned by a particular database user plus all tables to which the user has been granted access
USER_TABLES: All tables owned by a particular database user

NOTE:

• DBA_ views are available only when the database is open and running.
• Data contained in DBA_ views is static and is not cleared when the database is shutdown
• V$ views are available even when the database is not fully open and running.
• V$ views contain dynamic statistical data that is lost each time when the database is shutdown

Reference: Sybex Oracle Admininstration I Study Guide