HFS Plus
HFS Plus is a volume format (or disk file system) created by Apple Computer for storing files on hard disks and other types of storage devices. HFS Plus was first supported by Mac OS 8.1, released on January 19, 1998. HFS Plus is the name used by developers, but in user documentation the format is referred to as Mac OS Extended. HFS Plus was designed to replace Hierarchical File System (HFS) as the primary file system used with Macintosh computers.
HFS Plus is an improved version of HFS, supporting much larger files (64 bit length instead of 32 bit) and using Unicode (instead of MacRoman) for naming the items (files, folders). HFS Plus permits filenames up to 255 characters in length, and n-forked files similar to NTFS, though access to forks other than the data fork and resource fork requires use of separate APIs, for backward compatibility with HFS. HFS Plus also uses a full 32-bit allocation mapping table, rather than HFS's 16 bits. This was a serious limitation of HFS, meaning that no disk could support more than 65,536 sectors under HFS. When disks were small, this was of little consequence, but as they started to approach the 1GB mark, it meant that the smallest amount of space that any file could occupy (a single sector) became excessively large, wasting significant amounts of disk space. For example, on a 1GB disk, the sector size under HFS is 16KB, so even a 1-byte file would take up 16K of disk space.
Like HFS, HFS Plus uses B-trees to store most volume metadata.
With the release of the 10.2.2 update on November 11 2002, Apple added optional journaling features to HFS Plus for improved data reliability. These features were easily accessible in Mac OS X Server, but only accessible through the command line in the standard desktop client. However, in 2003 Mac OS X version 10.3 set all HFS Plus volumes on all Macs to be journaled by default.
