Nib file explained

Interface Builder 2.x. The NIB will take the form of a package of three files:
classes.nib, info.nib,and keyedobjects.nib. The last of these contains all the
information Cocoa needs to reconstitute objects for use in an application. The other
two files contain information about the class hierarchy and other settings that made it
possible to edit the NIB in IB 2.0; removing them produces a NIB package that is
usable,but not editable (unless you deselect “Flatten compiled XIB files” in your
target’s build settings). This form of NIB can be used on any version of Mac OS X,and
edited by IB 2 or 3.