Hi!

1, I do not intent to write code to export. Neither do any normal engineer/hobbiest. All we like to come up with some think that,
A, Work then its OK.
B, Work and can be exported then its good.
C, Work and is used again and again, then its excellent.
But still our major demand will be option A. And if it gots to B or C. Its usually our luck etc. Also remember that we are not writing program for PC, we write program for mcu, with usually fixed hardware.

2, I think that what 'satya srinivas' demand i.e. run code while EA connected to Vcc, is not possible in normal 89c51/52 etc. But you can integerate small functions in your internal flash ROM. And store your main program or part of main program in External ROM/RAM. The internal flash ROM will also be responsible to Interpret the external code. In few words "use your flash ROM to store driver routines and Interpreter routines. And use external memory to store program.