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HFS+ file system

By default. Mac OS X uses the HFS+ file system. You can force the install to use UFS, but you'll miss out on many features. The only thing I don't like about HFS+ is its arbitrary attitude toward case in file names. HFS+ is case preserving, but case insensitive. It's not fully integrated with the shell and that can cause confusion. If I

 mkdir appl
 cd Appl

I'll be in "appl". But that's not true for wild cards : I can't

 mkdir appl
 cd Ap*

Also, after making "appl", I cannot "mkdir Appl". This can cause problems with files brought from other Unix systems - although it is a little unusual, it is not unheard of to have two very different files whose names only differ in capitalization. Keep that in mind.

This has changed, see Case sensitivity in filesystems

You are also allowed to do such awful things as


Though Vi itself isn't going to put up with this "case doesn't matter" nonsense.

Update: Since 10.3, HFS+ optionally supports case sensitivity for file and folder names. However, you may run into other problems if you use that opion, because some utilities may still assume that names are insensitive.

But there's a lot to like about HFS+ beyond these gripes. Automatic defragmentation for small files, for example: if a file is under a certain size and is not otherwise being accessed and a few other conditions are met, it will automatically be relocated and defragmented on the fly (if necessary, of course) when it is opened. There's also "Hot file clustering" which tries to keep frequently accessed files under a certain size up at the beginning of the disk - keeping these things close together and at the most efficient access point (reads are longer at the outer sectors of a disk).

There's also the metadata, which lets tools like Spotlight and mdfind have extra power. While I have at times been annoyed enough at the case insensitivity confusion to consider reinstalling with UFS (or now with HFS+ and case sensitivity), I don't think I'll ever actually do so. You get used to the problems, and learn to avoid them.

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