What are predefined environment variables in Windows ?

Common predefined environment variables

%ALLUSERSPROFILE%  

C:\Documents and Settings\All Users

%APPDATA%  

C:\Documents and Settings\{username}\Application Data

%COMPUTERNAME%  

{computername}

%COMSPEC%   

C:\Windows\System32\cmd.exe

%HOMEDRIVE%   

C: %HOMEPATH% \Documents and Settings\{username}

%PATH%   

C:\Windows\System32\;C:\Windows\;C:\Windows\System32\Wbem

%PATHEXT%     

.COM; .EXE; .BAT; .CMD; .VBS; .VBE; .JS ; .WSF; .WSH

%PROGRAMFILES%       

Directory containing program files, usually C:\Program Files

%PROMPT%

Code for current command prompt format. Code is usually $P$G

%SYSTEMDRIVE%

The drive containing the Windows XP root directory, usually C:

%SYSTEMROOT%

The Windows XP root directory, usually C:\Windows %TEMP% and %TMP% C:\DOCUME~1\{username}\LOCALS~1\Temp

%USERNAME%

{username}

%USERPROFILE%

C:\Documents and Settings\{username}

%WINDIR%

C:\Windows

Some dynamic environment variables

%DATE%

Current date in the format determined by the Date command

%TIME%

Current time in the format determined by the Time command

%CD%

Current directory with its full path

%ERRORLEVEL%

Number defining exit status of a previous command or program

%RANDOM%

Random number between 0 and 32767