At database startup time, Oracle will only look for the password file in the ORACLE_HOME/dbs directory. The naming convention that Oracle will search for is: orapwSID. The SID must match the ORACLE_SID environment variable. If orapwSID can not be found, Oracle will look for a file named orapw. If Oracle can not find a orapw file you will get the ORA-01990 at database startup time.