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Archived - Mac OS: About Mac OS Extended Volume Hard Drive Format or HFS+

This article discusses the Mac OS Extended volume hard drive format, also referred to as HFS+.


Important: You should not use a Mac OS Extended formatted volume as your startup disk unless you have a Mac OS CD that is version 8.1 or later.

This article has been archived and is no longer updated by Apple.

Mac OS 8.1 Volume formats
Mac OS 8.1 and later supports a volume format named Mac OS Extended format. The hard disk format supported by Mac OS 8.0 and earlier is now referred to as the Mac OS Standard format. Mac OS Extended format optimizes the storage capacity of large hard disks by decreasing the minimum size of a single file. As an example, on a 4 GB hard drive a file containing only 4K of information requires 64K of space in Mac OS Standard format, whereas with the Mac OS Extended format, it will require the actual 4K on the 4 GB hard disk.

Always Backup Your Hard Disk Before Initializing
Whenever you initialize your hard disk, you must first back up your files. Initializing will erase all the data on the hard disk.

Mac OS Extended format is Supported by Mac OS 8.1 and Later
All computers must have Mac OS 8.1 or later installed to access the files on a Mac OS Extended format volume that is directly connected to the computer. If a Mac OS Extended format volume is connected to a computer running Mac OS 8 or earlier, you cannot see any of the files on the hard disk. A single document is accessible, explaining that your files are still on the hard disk but unaccessible. You will be able to access those files once you connect that hard disk to a computer running Mac OS 8.1 or later. However, Mac OS Extended formatted volumes shared on a network by a computer running Mac OS 8.1 or later can be seen by a computer running Mac OS 8 or earlier.

When to Choose Mac OS Standard instead of Mac OS Extended format
Volumes smaller than 32 MB can not be initialized as Mac OS Extended format; if you attempt this using the Drive Setup application it will state the "Initialization Failed." Floppy disks can not be initialized with Mac OS Extended format.

The storage efficiency of Mac OS Extended format typically applies to 1 GB or larger volumes.

How to Initialize with Mac OS Extended format
After backing up your data, you must initialize your hard disk to change the format from Mac OS Standard format to Mac OS Extended format. Always backup your hard disk before initializing. Initializing erases all the data on the hard disk. Once you have backed up your data, you can choose to use either of the following options to initialize the hard disk:

Option 1: In the Finder, select the hard disk you wish to initialize. Choose Erase Disk... from the Special menu. A dialog box will be displayed which contains a pop-up menu where you can select Mac OS Extended format.

Option 2: Open the Drive Setup application, version 1.4 or later. Choose Initialize. A dialog box will be displayed where you can specify Mac OS Extended format, as well as other initialization options.

Note: You must select the number of volumes in the Partitioning Scheme pop-up menu before selecting a volume format. Drive Setup can partition a disk into multiple volumes and each may have a different format.

After initializing, you may restore the data from your backup. After restoring, double-clicking on some aliases may result in the error "the original item could not be found". Locate the original file, and recreate the alias.

680x0 Specific Issues
680x0 processor computers cannot use a hard disk initialized with Mac OS Extended format as the start up disk, but the Mac OS Extended format can be used on additional disks connected to a 680x0 computer running Mac OS 8.1 or later. In addition, you can not select a hard disk initialized with Mac OS Extended format in the Virtual Memory section of the Memory control panel.

Can I Format my Server's Hard Disk as Mac OS Extended format if my Client Computers Have an Earlier Version of Mac OS?
Yes. The server may use Mac OS 8.1 and Clients may have earlier versions of Mac OS. The clients can still access all files on the server's Mac OS Extended formatted hard disks.

Text Encoding Converter Extension and Text Encoding Folder
WARNING: Proper installation of Mac OS 8.1 automatically places the Text Encoding Converter extension and the Text Encoding folder in the System Folder. In order for Mac OS Extended format to function properly, you must not move or delete these files.


Frequently Asked Questions about the Mac OS Extended format

What is Mac OS Extended format?
Mac OS Extended format is a hard disk format that increases the number of allocation blocks on the disk. This format also allows more than 65,000 files on the hard disk. Mac OS Extended format optimizes the storage capacity of large hard disks by decreasing the minimum size of a single file.


What are the differences between Mac OS Extended format and Mac OS Standard format?
The most visible difference between Mac OS Extended format and Mac OS Standard format, other than the minimum file size, is the maximum number of files.


How do I know a hard disk is Mac OS Extended format?
Select the hard disk in the Finder and choose the Get Info command in the File menu. The format information will specify either Mac OS Standard or Mac OS Extended.


Should I reformat my hard disk to be Mac OS Extended format?
Mac OS Extended format is most useful for hard drives that are 1 GB or larger. Do not reformat a hard disk with Mac OS Extended format if it is intended to be used as the startup disk for a computer with a 680x0 processor.


Can I use my third party disk utilities with a Mac OS Extended format hard disk?
Some third party utilities may not be compatible with hard disk initialized with Mac OS Extended format. Consult the utility's documentation, or contact the vendor for compatibility information.


Where can I get more information on Mac OS Extended format?
Both Apple Guide and Mac OS Info Center have information on this hard disk format. Choose the Help menu or double-click on the Mac OS Info Center icon on the desktop to access Mac OS Extended information.

Last Modified: May 10, 2012
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  • Last Modified: May 10, 2012
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