HFS Plus

HFS Plus, also called Mac OS Extended, is a file system developed by Apple for Macintosh computers. It replaced the original Hierarchical File System and stores files using Unicode names and a hierarchical catalog.

HFS Plus volume format: The on-disk arrangement of HFS Plus headers, allocation data, catalogs, and other metadata. Shows how the file system lays out its essential structures on a volume.
B-tree: A balanced search tree designed to keep ordered data accessible with few storage reads. HFS Plus uses B-trees to index catalogs, extents, and attributes.
Mac OS 8: A version of Apple's Macintosh operating system released in 1997. HFS Plus debuted with Mac OS 8.1 in 1998, during this operating system's era.
Mac OS X: Apple's desktop operating system family that succeeded classic Mac OS. Mac OS X used HFS Plus as its principal file system for many years.
HFS Plus catalog file: A B-tree database in HFS Plus that records files, folders, and their relationships. Its records provide the hierarchical namespace used to locate files.
Unicode: A standard that assigns consistent character codes to writing systems and symbols. HFS Plus encodes filenames in Unicode rather than relying only on legacy Mac character sets.
Mac OS 8.1: An update to Mac OS 8 released in 1998 that introduced HFS Plus support. It was the first Macintosh operating system release to support HFS Plus.
Time Machine: Apple's backup software, introduced with Mac OS X Leopard. Traditional Time Machine backups on local disks have commonly used HFS Plus volumes.
HFS Plus allocation file: A bitmap in HFS Plus that tracks which allocation blocks are in use. It identifies available space when files grow or new files are created.
Allocation unit: The smallest region of storage that a file system allocates to a file. HFS Plus tracks free and occupied allocation blocks to manage volume space.

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Universal Disk FormatCompared with: It illustrates a platform-associated filesystem alternative to UDF’s optical-media focus.