ARCHIVED: What is the Mac OS Extended Format?

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The Mac OS Extended Format, also known as HFS+, is the primary volume format for Mac OS X. Some of its features include:

Because it uses a 32-bit address to store data, HFS+ can assign more than four billion allocation blocks to a volume. As a consequence, the minimum file size for even very large volumes remains small, usually around 4KB. With some HFS+ formatting utilities, the minimum file size is as little as 512 bytes (i.e., a single logical block).
It supports Unicode and filenames of up to 255 characters.
It supports journaling by default, which provides protection against power outages and hardware component failures and reduces the need for repairs.
Mac OS Extended volumes can optionally be formatted for case sensitivity. This allows for different filenames that have the same characters, but different case (e.g., Dog would be different from dog). This makes it more like formats used in other Unix operating systems.