This publication describes the process and products I created when I decided to design and program an enhanced Disk Operating System (DOS) for my Apple //e. Wherever I am able, I have included code samples, schematic diagrams, equations, figures, tables, and representative screen shots to help explain what I have created and the reasons why I did so. As in my previous design of an Apple ][ DOS, i.e. DOS 4.1L and DOS 4.1H that I released in 2018, this has been an incredible journey for me. With DOS 4.3, I have again re-imagined that time when I mostly lived, breathed, and worked on Apple ][ hardware and software development continuously for a good period of my life many, many years ago. The list that follows are some of the features that I have engineered into the DOS 4.3 File Management System. DOS 4.3 boots directly into Language Card memory and sets HIMEM to 0xBE00. All five file buffers are fully contained in Language Card memory. DOS 4.3 supports the full integration of the Lisa and Big Mac assemblers in Auxiliary Memory. Both assemblers now support the full 65C02 instruction set. Sourceror and Big Mac both support all SWEET16 opcodes. My ROM image supports the 65C02, SWEET16, and GARBAGE based on Bongers' algorithm. DOS 4.3 supports most Clock Cards which play an integral role in Volume and File timestamps. Volumes may be titled, numbered, locked, and initialized to boot or to store data exclusively. Even track 0x00 is used for data. Files are loaded and saved using an acceleration algorithm. DOS 4.3 supports Applesoft CHAIN, File DIFF, File GREP, File LIST, File Undelete, Sector Display, Sector Modify, Syntactical HELP, DOS Processing Control, Variable Management, Half-Phase Tracking, and full lowercase command and argument input. DOS 4.3 copies files using a modified FID that accepts Volume and Phase Number parameters. DOS 4.3 can read DOS 3. Volumes and files. DOS 4.3 can initialize Volumes with up to 48 tracks having either 16 or 32 sectors per track. All the source code and all the schematics can be requested through www.applecored.net.