# What is a filesystem?

A hard drive is initially just one big empty space with no organization. To be made useful, a drive must be "formatted" in a particular way so that information can be stored and later retrieved. The particular organization applied is called the filesystem.

One analogy would be a big, empty parking lot. To be made useful, lines should be painted on the ground indicating where the cars should park. However, there are many different ways that a given space can be painted, involving many diverse attributes like the size of the spaces, the orientation (side-by-side or parallel parking), how the rows are organized, how many rows, and so on. Different systems have different ideas on how this should be done, so there are many different filesystems used in practice.

The standard filesystem for Mac OS X is called HFS+, or HFS Extended. The most common filesystem used on Windows machines is called NTFS.