Many people are saying that Apple has restricted it for better performance. If so Apple should increase the size of RAM to support multitasking. So Apple is not allowing it.
Others say that Cocoa Touch applications can’t be multitasking as the iPhone has only one window and views on it.
I can not understand which is the actual reason for this ?
Please clarify me.
Multitasking is supported on the iPhone. Apple’s applications can run in the background. Also you can run multiple threads within the same app.
What is not allowed is 3rd party apps running in the background. Why? Frankly, no one will be able to tell you. They will be straight up guessing as it was Apple’s decision to not allow this at the current moment, and Apple never gave reasons why.
Edit: Also see this video about iPhone OS myths regarding multitasking.