I started out doing AppleTalk Filing Protocol (AFP) for Apple IIs. Then some client-side work on AppleTalk Secure Data Stream Protocol. Then various other Apple II file systems. Did various file system work for the failed Copland project. Then co-designed and co-developed HFS Plus for MacOS 8.1. Worked on various Mac OS and Mac OS X file systems, including FAT, NTFS, exFAT, HFS, and APFS. Built the migration tool to convert HFS Plus to APFS, in place.