Summary:

• ~/ - the root directory
• ~/bin - contains OS executable files
• ~/dev - IO devices like flash drives
• ~/etc - admin files
• ~/lib - installed executables, by user
• ~/lib64 - 64 bit executables
• ~/tmp - temporary directory
• ~/usr/bin - another /bin directory, user-specific
• ~/usr/bin/x11 - GUI files
• ~/usr/lib - another user specific /lib
• ~/usr/ucb - contains university of berkeley files
• ~/u - contains user home directory
• ~/var - contains variable length files

Details:

The disk that the operating system is installed on is mounted at /, or the root directory. Another abbreviation for this is ~, to indicate in case of duplicate directories. The /bin directory contains all executable files standard to installations. The /dev directory contains directories that represent all input and output devices, but is usually used for additional storage devices. The /etc directory contains miscellaneous administrative files, such as the password file or startup files. The /lib directory contains all additional programs installed on the host. This also applies to the /lib64 directory found in 64 bit hosts. The /tmp directory is a temporary directory used by programs and users, but should usually be empty. The /usr/bin directory can either be a redirection to the /bin directory or contain less common executable files, depending on the particular distribution of unix. The /usr/bin/x11 directory contains files used for the graphical user interface. The /usr/lib directory is similar to the /usr.bin directory, except that it redirects to the /lib directory and contains less frequently used executable files. The /usr/local directory contains files installed by local administrators. The /usr/ucb directory contains utilities created by Berkeley University. The /u directory contains user home directories. The /var directory is used to store variable length files, such as print spool files.