Hierarchical File System (HFS), is a file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. HFS is also referred to as Mac OS Standard (or, erroneously, “HFS Standard”), where its successor, HFS Plus, is also called Mac OS Extended (or, erroneously, “HFS Extended”).