Windows environment variables

Below is a list of Windows environment variables and an explanation of their function.
 * ALLUSERSPROFILE: path to the "All Users" directory
 * APPDATA: path to the current user's "Application Data" directory
 * CLIENTNAME
 * CommonProgramFiles: path to the "Common Files" directory
 * COMPUTERNAME: computer name
 * ComSpec: path to the executable of the command line prompt
 * HOMEDRIVE: drive letter of the homedrive
 * HOMEPATH: path to the user's personal directory
 * LANG: language used by the operating system
 * LOGONSERVER: name of the server which authenticated the current user — typically is "\\%COMPUTERNAME%"
 * OS: name of the operating system
 * NUMBER_OF_PROCESSORS: number of processors of the computer
 * PROCESSOR_ARCHITECTURE: processor architecture, values might be x86 and x64
 * PROCESSOR_IDENTIFIER: contains some information on the processor
 * PROCESSOR_LEVEL: The model number of the processor.
 * PROCESSOR_REVISION
 * ProgramFiles: path to the "Program Files" directory
 * SESSIONNAME
 * SystemDrive: value of the drive containing the system folder (usually "C:")
 * SystemRoot: path to the system folder (ex: "C:\Windows")
 * TEMP: path to the current user's "Temp" directory, the directory where temporary files are stored
 * TMP: path to the current user's "Temp" directory, the directory where temporary files are stored (same value as TEMP)
 * USERDOMAIN: name of the domain to which the current user belongs, which is often the computer's name
 * USERNAME: username of the current user
 * USERPROFILE: path to the current user's profile directory (such as "C:\Users\%USERNAME%" in Vista and Windows 7)
 * windir: path to the "WINDOWS" directory