File systems under Mac OS X Mac OS X
uses a file system that it inherited from classic Mac OS
called HFS Plus
. HFS Plus is a metadata
-rich and case preserving
file system. Due to the Unix roots of Mac OS X, Unix permissions were added to HFS Plus. Later versions of HFS Plus added journaling
to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter.
Filenames can be up to 255 characters. HFS Plus uses Unicode
to store filenames. On Mac OS X, the filetype
can come from the type code
, stored in file's metadata, or the filename.
HFS Plus has three kinds of links: Unix-style hard links
, Unix-style symbolic links
. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in userland
Mac OS X also supports the UFS
file system, derived from the BSD
Unix Fast File System via NeXTSTEP
. However, as of Mac OS X 10.5 (Leopard), Mac OS X can no longer be installed on a UFS volume, nor can a pre-Leopard system installed on a UFS volume be upgraded to Leopard.