What is the difference between NIB and XIB Interface Builder file formats?

Question

What is difference between nib and xib in Interface Builder files?

Answer 1

As of Interface Builder version 3, a new file format (with extension .xib) has been added, which is functionally identical to .nib, except it is stored in a flat file, making it more suitable for storage in revision control systems and processing by tools such as diff.

http://en.wikipedia.org/wiki/Interface_Builder#Design