1 Introduction The Hierarchical Disc Filing System, HDFS, which this manual describes is designed to work with the Intel 8271 Floppy Disc Controller chip fitted in older BBC microcomputers. It is compatible with the Acorn 1.20 DNFS and provides some extra functionality. This manual will assume that the user is familiar with the operation of disc drives, and that the disc interface, disc drive(S) and ROM are installed (see appendix B for details of how to install the ROM). A simple introduction to floppy discs can be found in appendix A. Users who are familiar with the Acorn 1.20 DNFS should read the next section, which will outline the major differences between HDFS and the DNFS. Users not familiar with the DNFS should miss out this section on first reading.