Instance parameter file location

When an instance starts up,
it reads it's parameter file initSID.ora. But I've got one in $ORACLE_BASE/admin/$ORACLE_SID/pfile and one in $ORACLE_HOME/dbs.
Where an instance looks for it's parameter file should be in the operating system specific Oracle manual. I can't find it.

I'm using Oracle7 7.3.2.2 on HP-UX 10.20.

--
Ludo Joris
RUCA - University of Antwerp, Belgium
lujo_at_ruca.ua.ac.be