ORACLE_HOME

ORACLE_HOME refers to either:

    a directory where the Oracle software is installed; or
    an environment variable pointing to the directory where the Oracle software is installed.


Windows

Check current value:

echo The current ORACLE_HOME is %ORACLE_HOME%

Set the ORACLE_HOME environment variable:

set ORACLE_HOME=C:\oracle\ora10.2

On Windows the ORACLE_HOME may also be stored in the registry:

    HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE
    HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOMEID
    HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\ALL_HOMES
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services

http://www.orafaq.com/wiki/ORACLE_HOME