Server Administration :: Difference Between V_$ And V$ Views

difference between V$ and V_$ views. It looks same to me. lets take the example of V$LOG and V_$LOG , both views returns same set of columns when described.

SQL> desc V$LOG
Name Null? Type
----------------------------------------- -------- -----------------
GROUP# NUMBER
THREAD# NUMBER
SEQUENCE# NUMBER
BYTES NUMBER
MEMBERS NUMBER
ARCHIVED VARCHAR2(3)
STATUS VARCHAR2(16)
FIRST_CHANGE# NUMBER
FIRST_TIME DATE

SQL> desc V_$LOG
Name Null? Type
----------------------------------------- -------- -----------------
GROUP# NUMBER
THREAD# NUMBER
SEQUENCE# NUMBER
BYTES NUMBER
MEMBERS NUMBER
ARCHIVED VARCHAR2(3)
STATUS VARCHAR2(16)
FIRST_CHANGE# NUMBER
FIRST_TIME DATE