External and Output Columns in OLEDB datasource

Hi,

             Can any one tell me,what is the difference between data type changing option in External Column and Output column in Advanced editor of OLEDB Source? If i want to change datatype of one of my column,whether i need to change both? Same thing is there in OLEDB Destination as well.But there input column datatype is not active.Can ny one explain?

Image may be NSFW.
Clik here to view.