Difference between revisions of "HFS+"

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There are structurally many differences between HFS and HFS+, which are listed below[http://developer.apple.com/technotes/tn/tn1150.html#HFSPlusBasics]:
 
There are structurally many differences between HFS and HFS+, which are listed below[http://developer.apple.com/technotes/tn/tn1150.html#HFSPlusBasics]:
 
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An HFS+ volume contains five special files that are necessary to the file system:
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An HFS+ volume contains five special files:
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Catalog file
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Catalog file - Describes the folder and file hierarchy of the volume. It is organized as a "balanced tree" for fast and efficient searches
 
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<li>Extents overflow file
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<li>Extents overflow file - Additional extents (contiguous allocation blocks allocated to forks) are stored in a b-tree in this file
 
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</li>
 
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Allocation file
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Allocation file - Specifies whether an allocation block is free (similar to $Bitmap in NTFS). This is stored in a bitmap, specifying a free allocation block with a "clear bit"
 
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<li>Attributes file
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<li>Attributes file - Contains attribute information regarding files or folders
 
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Startup file
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Startup file - Allows computers to boot that do have built in support for HFS+ file systems
 
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Revision as of 20:03, 28 November 2006

HFS+, or Hierarchical File System Plus, is the file system designed by Apple Computer[1] to supersede HFS. First introduced with Mac OS 8.1, one of the biggest differences was the lower allocation block size of 4kb, thereby increasing performance and lowering fragmentation [2].

There are structurally many differences between HFS and HFS+, which are listed below[3]:

Feature

HFS

HFS Plus

Benefit/Comment

User visible name

Mac OS Standard

Mac OS Extended

Number of allocation blocks

16 bits worth

32 bits worth

Radical decrease in disk space used on large volumes, and a larger number of files per volume.

Long file names

31 characters

255 characters

Obvious user benefit; also improves cross-platform compatibility

File name encoding

MacRoman

Unicode

Allows for international-friendly file names, including mixed script names

File/folder attributes

Support for fixed size attributes (FileInfo and ExtendedFileInfo)

Allows for future meta-data extensions

Future systems may use metadata for a richer Finder experience

OS startup support

System Folder ID

Also supports a dedicated startup file

May help non-Mac OS systems to boot from HFS Plus volumes

catalog node size

512 bytes

4 KB

Maintains efficiency in the face of the other changes. (This larger catalog node size is due to the much longer file names [512 bytes as opposed to 32 bytes], and larger catalog records (because of more/larger fields)).

Maximum file size

231 bytes

263 bytes

Obvious user benefit, especially for multimedia content creators.


An HFS+ volume contains five special files:

  1. Catalog file - Describes the folder and file hierarchy of the volume. It is organized as a "balanced tree" for fast and efficient searches
  2. Extents overflow file - Additional extents (contiguous allocation blocks allocated to forks) are stored in a b-tree in this file
  3. Allocation file - Specifies whether an allocation block is free (similar to $Bitmap in NTFS). This is stored in a bitmap, specifying a free allocation block with a "clear bit"
  4. Attributes file - Contains attribute information regarding files or folders
  5. Startup file - Allows computers to boot that do have built in support for HFS+ file systems