Hierarchical File System (HFS)

Hierarchical File System (HFS) is the file system used by Mac Operating System and developed by Apple Inc. At the beginning, HFS was designed to work on floppy, CD-ROMs and hard disk drives. HFS is referred as a standard for Mac Operating System and the successor of HFS i.e. HFS Plus is also known as HFS Extended.

Components of Macintosh File

File stored on Macintosh Operating System contains two forks:

  • Resource Fork: This component is an indexed file which contains code segments, dialog boxes, menu items etc.
  • Data Fork: This component contains a stream of bytes.

Each and every fork in a file comprises of one or more extents of blocks, which encodes the extent’s starting block and the size. A file’s catalog record contains a file’s first extent of a fork. The further extents getting stored on the Mac are saved in the form of B-Tree.

Each files stored on the HFS file system have an identification number. A file is named based on its parent’s identification number and directory’s file name, as it is of 32 character string which also contains nulls.

The new catalog B-Tree is different from traditional B-Tree structure, as all the nodes at each level are linked together to form a doubly linked list, with the records at the leaf nodes.


The technique which is used to protect the integration of Mac Operating System Extended file systems on Mac Operating System X volumes is known as Journaling. When the journaling process in enabled, it keeps track and record of each and every functionalities going on the system.

If your system is functioning well due to data loss scenario like power fluctuations or virus attack, journal file will help you to restore back to the same state after restarting server.

Journaling is most important and best feature to use for servers with many number of files and high availability.

Related Information

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