DirectCast requires the run-time type of an object variable 
to bethe same
 as the specified type.The run-time performance 
ofDirectCast is better 
than that of CType, if the specified type and the run-time 
typeof the 
expression are the same.
Ctype works fine if there is a valid conversion defined 
between the 
expression and the type.

The difference between the two keywords is that CType 
succeeds as long as there is a valid conversion defined 
between the expression and the type, whereas DirectCast 
requires the run-time type of an object variable to be the 
same as the specified type. If the specified type and the 
run-time type of the expression are the same, however, the 
run-time performance of DirectCast is better than that of 
CType. DirectCast throws an InvalidCastException error if 
the argument types do not match.

Direct cast: Supports only reference type conversions
             it throws exception

CType cast: supports only Value type conversions