HFS+ Overview

The Mac OS Extended Volume Hard Drive Format, otherwise known as HFS+, is the file system found on Mac OS 8.1 and later, including Mac OS X. It is an upgrade from the original Mac OS Standard Format known as HFS (HFS Standard), or Hierarchical File System, supported by Mac OS 8.0 and earlier.

Overview

Mac OS Extended format (HFS+) is a hard disk format introduced on January 19, 1998, by Apple Inc. to replace their HFS and the primary file system in Macintosh computers and iPod music players.

Up from HFS, HFS+ increases the number of allocation blocks on the disk and decreases the minimum size of a file, thus optimizing the storage capacity of a large hard disk.

Therefore, HFS+ allows for a larger maximum number of files than its' HFS counterpart. Note the difference between HFS and HFS+ in the following example:

Example:

On a 4 GB hard drive, a file containing 4 KB of information would require 64 KB of space with HFS. With HFS+, it would only require 4 KB on the 4 GB hard drive. This is because the HFS allocation block size would be 16 KB and HFS+'s increased number of allocation blocks of the disk and the decreased minimum size of the blocks allows for less wasted space.

HFS+ also supports much larger files than HFS, with 32-bit block addresses as opposed to HFS's 16-bit length.

It uses Unicode to name files, encoded in UTF-16 and normalized to a form similar to Unicode Normalization Form D (NFD).

HFS+ permits file names of up to 255 UTF-16 characters in length and n-forked files. HFS+ uses a 32-bit allocation mapping table, as opposed to HFS's 16-bit table. Also, unlike most other file systems; HFS+ supports hard links to directories. HFS+ uses B-trees to store most volume metadata.

HFS+ File Limits in Mac OS X: