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MAC Hard Drive Data Recovery

About Apple Mac File Systems

HFS (the Hierarchical File System) was developed for use on the Apple Mac for the storage of files on hard drives and floppy drives, and is also used as the file system on R/W optical disks, CD and DVD. Introduced by 1985 HFS replaced MFS (the Macintosh File System). Compared with the DOS FAT file system that was used on the majority of PC Systems, HFS was highly sophisticated. Each file had a unique reference number, in the way that UNIX files were referenced by an inode number, with the file name being an attribute of the file rather then the key identifier (as in FAT). Files could also have multiple streams (known as forks), so a file could have a data fork, and a resource fork.

HFS is based around a central file, the catalog file, whose contents is a B-tree hierarchy. There remained a limit of 65,536 files within an HFS file system. The key block in HFS is the Master Directory Block which describes the critical elements of the file system a second copy of which resides at the opposite end of the file system.

Towards the end of the 1990s the HFS+ (HFS Plus) file system was introduced. Originally the HFS+ file system was contained within a single file in an HFS file system, HFSX which came later was truly a standalone file system and not contained within this HFS "wrapper". HFS+ increased the number of files that could be stored and made a number of additional improvements relating to file allocation, as well as using unicode for file names which greatly increased flexibility.

The introduction of OSX (MAC OS 10) saw Apple move to a version of Linux with HFS and HFS+ still supported but with additional support for other file systems including NTFS (read-only) and UFS.

MAC Hard Drive Data Recovery

The key to HFS and HFS+ data recovery is being able to access or salvage the catalog. Both HFS and HFS+ use a central catalog file and without access to the elements within this there is little opportunity to recover any files. Since the most common problems are either hardware related with bad sectors, or localised corruption, is is uncommon to lose the entire catalog unless the damage is so widespread as to also impact large numbers of files. Data recovery from HFS and HFS+ volumes is, therefore, usually highly successful except where massive hardware failure are involved.

Last Updated (Tuesday, 09 June 2009 15:51)

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