iPhone application development and iPad application development is the difference?

Trouble you, I want to be a program project can run on the iPhone and iPad, respectively. Can you tell me the difference between developed and detailed attention between items them? ? Very grateful!
Reply:
UI picture size to note ....
The most important is this part
The second is to use iAD, then, to remember that iPad is 3.2SDK
iAD 4.0 SDK is only something ....
Reply:
Difference is no difference. . . .
Reply:
It should be the same, after all, developed using xcode
Reply:
It should be the same, after all, developed using xcode