Cocoa versus Cocoa Touch - What is the difference?
Application Framework For
i) Cocoa is the application framework for Mac OS X.
ii) Cocoa Touch is the application framework for iPhone and iPod Touch.
Frameworks
i) Cocoa: Foundation and AppKit.
ii) Cocoa Touch: Foundation and UIKit
Absence of certain classes
Cocoa has NSHost and Cocoa Touch doesn't
API
i) Cocoa: All the classes used in Cocoa have the NS prefix Ex: NSTextField
ii) Cocoa Touch: classes used in Cocoa have the UI prefix Ex: UITextField
MVC patterns
i) Cocoa: Cocoa has multiple alternative design patterns – in addition to MVC
ii) Cocoa Touch: The iPhone SDK has a reinforced MVC system, which performs better than the default MVC in Cocoa
Other Differences
There Are also Differences In App Lifecycle, Sandboxing ,Memory Footprint
Links:
http://teks.co.in/site/blog/cocoa-vs-cocoa-touch-beginners-guide/
http://iphonenativeapp.blogspot.in/2011/02/difference-between-cocoacocoa-touch-and.html
https://iphonecodecenter.wordpress.com/tag/difference-between-cocoa-cocoa-touch/
Cocoa is commonly referred to as the combination of the Foundation and AppKit frameworks, while Cocoa Touch is the combination of the Foundation and UIKit frameworks.
Cocoa and Cocoa Touch sit on top of other collections of frameworks to create the API stacks. The other layers are Media, Core Services and Core OS.
The main difference between Cocoa and Cocoa touch is that the UI classes and APIs aren't the same as Mac OS X’s and macOS’s, so instead of NSTextField, you have UITextField. Many of the classes share the same functionality and can be ported quite easily by simply changing the class name, though most will require some more changes, but usually nothing too heavy.
There are also some differences between the Foundation frameworks in Cocoa and Cocoa Touch, most commonly missing classes, for example, Cocoa has NSHost and Cocoa Touch doesn't.
You will come to know more of the nuances between the two and will soon be able to instinctively know what will work on an iPhone with little/no modification and what will require some work to port between, but it's not that difficult.