Developing Apps for iPhone and iPad

While both iPhone and iPad are from Apple and have the same underling OS and it is possible to run applications built for iPhone to be installed on iPad as well, porting iPhone apps to iPad is not a straight forward exercise.

In principle, the same app can run, however the user experience will not be great and will not meet the expectations of the use as the larger real estate on iPad will not be efficiently used.

Also, there are some fundamental differences between the two which have to be kept in mind while developing the applications:

Features	iPhone	iPad
Phone	Yes	No
Camera	Yes (2 for video conferencing in iPhone 4)	No
Screen Size	3.5 inch display	9.7 inch display
Resolution	960 x 480	1024 x 768
GPS	Yes	only on Wi-Fi supported Models
Sensors	Gyroscope	No Gyroscope

Every app needs to consider the Screen size and Resolution as the major difference. However apps that include phone features, GPS or Camera features will have to be rewritten for iPad. 

Also, the lack of gyroscope in iPad makes it not so very suitable for gaming apps.