Difference

Hi Swetha,

External Procedure Calls :

In an external procedure call, the called unit is not part of the calling program. This means that, at runtime, an extra program has to be loaded into the internal session of the calling program. You can use external calls for procedures and subscreens.

The additional loaded program is an instance with its own global data area. When you call an external subroutine, the calling program and the loaded program form a single program group, unless the loaded program is a function group. Function groups always form their own program group. Furthermore, when you call methods externally, they and their class form their own program group. Within a program group, interface work areas and the screens of the calling program are shared. Classes cannot contain interface work areas.

See this link

http://help.sap.com/saphelp_nw04/helpdata/en/10/e7dbe482ba11d295a40000e8353423/frameset.htm

External Program Calls :

In an external program call, the unit that you call is an independent ABAP program. At runtime, the called program is loaded into its own internal session in the current external session. Any program that can have its own screens can be called in an external program call. The most usual external program calls are for executable programs and transactions assigned to a module pool.

See this link:

http://help.sap.com/saphelp_nw04/helpdata/en/10/e7dbe782ba11d295a40000e8353423/frameset.htm

Plzz Reward if it is useful,

Mahi.