pasted from: http://osxdaily.com/2007/03/30/mac-os-x-directory-structure-explained/
If you have ever looked at your Mac’s root directory and wondered what some of those other directories are for, you’re probably not alone. Mac OS got a whole lot more complex with the advent of OS X, adapting a unix file structure that is largely unfamiliar to Mac OS 9 and Windows users. So just what is /System, /Library, /usr, and all the others for anyway? Here’s a brief explanation of each directory as found in Mac OS X.
By default, if you look in the root of your Mac’s hard disk you’ll see some unfamiliar sounding directories. From the command line, you will see even more if you type ls /. Explained in no particular order:
| Directory | Description |
| /Applications | Self explanatory, this is where your Mac’s applications are kept |
| /Developer | The Developer directory appears only if you have installed Apple’s Developer Tools, and no surprise, contains developer related tools, documentation, and files. |
| /Library | Shared libraries, files necessary for the operating system to function properly, including settings, preferences, and other necessities (note: you also have a Libraries folder in your home directory, which holds files specific to that user). |
| /Network | largely self explanatory, network related devices, servers, libraries, etc |
| /System | System related files, libraries, preferences, critical for the proper function of Mac OS X |
| /Users | All user accounts on the machine and their accompanying unique files, settings, etc. Much like /home in Linux |
| /Volumes | Mounted devices and volumes, either virtual or real, such as hard disks, CD’s, DVD’s, DMG mounts, etc |
| / | Root directory, present on virtually all UNIX based file systems. Parent directory of all other files |
| /bin | Essential common binaries, holds files and programs needed to boot the operating system and run properly |
| /etc | Machine local system configuration, holds administrative, configuration, and other system files |
| /dev | Device files, all files that represent peripheral devices including keyboards, mice, trackpads, etc |
| /usr | Second major hierarchy, includes subdirectories that contain information, configuration files, and other essentials used by the operating system |
| /sbin | Essential system binaries, contains utilities for system administration |
| /tmp | Temporary files, caches, etc |
| /var | Variable data, contains files whose contents change as the operating system runs |
If we forgot anything, or if something isn’t properly described, feel free to chime in with comments.
