Apple introduced new resource file format in Xcode 3.0: **.xib**.
Xib files are used during development time only and are will be converted to deployment format (compressed .nib) at build time.
The main benefit of .xib is that it is text-based. Text makes it easier to work with .xib files stored in a source control system.
Here is quick way to convert all old .nib files to .xib format:
`ls | grep nib | xargs -L1 ibtool --upgrade`
