Why Truncate is faster :-

TRUNCATE is much faster than DELETE.When you type DELETE.all the data get copied into the Rollback Table space first.then delete operation get performed .Thatswhy when you type ROLLBACK after deleting a table ,you can get back the data(The system get it for you from the Rollback Tablespace).All this process take time.But when you type TRUNCATE,it removes data directly without copying it into the Rollback Table space.Thatswhy TRUNCATE is faster.Once you Truncate you cann't get back the data.