Here are the differences between data dictionary views and V$ views, in Oracle.
|Data Dictionary views||V$ views|
|Data will not be lost even after instance is shutdowned||Data will be lost if instance is shutdowned|
|Will be accessible only if instance is OPENED||(some are) Will be accessible even if instance is in mount or nomount stage (STARTED)|
|Data dictionary view names are plural||V$ view names are singular|