In early versions of Mac OS X, Address Book archives were stored as ABBU files, a format unique to Apple computers and practically useless anywhere else. Since the Contacts app in OS X Mavericks -- which replaced the Address Book -- supports both ABBU and CSV formats, you can use the Contacts app to quickly convert an Address Book backup to CSV format.
Video of the Day
Launch the Contacts app on your Mac.
Go to the "File" menu at the top of the screen and select the "Import" command.
Highlight the ABBU file you want to convert and click "Open" to add it to your Address Book data.
Click the "File" menu, select "Export," then "CSV." Contacts creates a new archive file in CSV format. Use this file in any app on a Mac or Windows PC to import the address book data.