Bv Control for Oracle looks at many different locations to fetch the value of $ORACLE_HOME environment variable.

For Oracle on Unix OS:

1. Firstly it reads the Oratab file located in /etc directory on Linux OS or /var/opt/oracle on Solaris OS.

2. If the Oratab file is not accessible or entry for $ORACLE_HOME, it queries the MGMT$TARGET_COMPONENTS table in SYS schema in the Oracle data dictionary.

3. If the value is not present in the MGMT$TARGET_COMPONENTS table in SYS schema, it reads the value of ORACLE_HOME from the $ORACLE_HOME environment variable.

4. If the value of $ORACLE_HOME environment variable is not set, it reads the Listener.ora file.
 

For Oracle on Windows OS:

1. It reads the Registry key ORACLE_HOME from the registry path 'HKEY_LOCAL_MACHINE -> SOFTWARE -> ORACLE -> KEY_OraDb10g_home1'.

2. If the ORACLE_HOME key is not defined in the registry or is not accessible, it queries the MGMT$TARGET_COMPONENTS table in SYS schema in the Oracle data dictionary.

3. If the value is not present in the MGMT$TARGET_COMPONENTS table in SYS schema, it reads the value of ORACLE_HOME from the $ORACLE_HOME environment variable.

4. If the value of $ORACLE_HOME environment variable is not set, it reads the Listener.ora file.