HFS Plus permits filenames up to 255 characters in length, and n-forked files similar to NTFS, though until 2005 almost no system software took advantage of forks other than the data fork and resource fork.
HFS Plus also uses a full 32-bit allocation mapping table rather than HFS's 16 bits, significantly improving space utilization with large disks.
HFS Plus volumes are divided into sectors (called logical blocks in HFS), that are usually 512 bytes in size.
These sectors are then grouped together into allocation blocks which can contain one or more sectors; the number of allocation blocks depends on the total size of the volume.
HFS Plus's system greatly improves space utilization on larger disks as a result.
File and folder names in HFS Plus are also character encoded in UTF-16 and UTF-16 implies that characters from outside the Basic Multilingual Plane also count as two code units in an HFS filename).
It is also referred to as Mac OS Extended or HFS Extended, where its predecessor, HFS, is also referred to as Mac OS Standard or HFS Standard.
In open source and some other areas this is referred to as Apple FSCompression.
With the release of the Mac OS X 10.2.2 update on November 11, 2002, Apple added optional journaling features to HFS Plus for improved data reliability.
These features were accessible through the GUI, using the Disk Utility application, in Mac OS X Server, but only accessible through the command line in the standard desktop client.
Until the release of Mac OS X Server 10.4, HFS Plus supported only the standard UNIX file system permissions; however, 10.4 introduced support for access control list–based file security, which provides a richer mechanism to define file permissions and is also designed to be fully compatible with the file permission models on other platforms such as Microsoft Windows XP and Windows Server 2003.
In Mac OS X Leopard 10.5, directory hard-linking was added as a fundamental part of Time Machine.