Chapter 7. Filesystem Overview

This chapter examines how Mac OS X works with files, both in the lower level of its filesystems, and more generally in the specific directory layouts it uses to organize its most important files and keep track of installed applications.

Mac OS X Filesystems

Like earlier versions of Mac OS, Mac OS X filesystems favor the Mac OS Extended Format, better known as HFS+ (Hierarchical File System),[2] but they also work well with the Universal File System (UFS) that most other Unix-based operating systems use as their primary filesystem.

Most Mac OS X volumes use HFS+ as their format for two reasons. First, until Mac OS X 10.3, HFS+ has performed much better than UFS (though UFS performance in Panther has improved greatly, close to matching that of HFS+). The other reason is that HFS+ natively supports multiple file forks (see Section 7.1.2.) Still, through strong UFS support, a Mac OS X machine can work seamlessly with other Unix volumes, such as network-mounted ones that may be accessible over NFS.

Differences Between HFS+ and UFS

Here are the most noticeable differences between the HFS+ and UFS file formats:

  • UFS is case-sensitive in its file path interpretation, while standard HFS+ is not. The paths /tmp/foo, /tmp/Foo, and /TMP/FOO all point to the same location on an HFS+ system but to three different ones on a UFS filesystem. However, using Mac OS X Server 10.3, you can format case-sensitive HFS+ volumes, and these volumes will maintain case-sensitivity ...

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