When PGA_AGGREGATE_TARGET parameter is set oracle 9i will ignore all of the PGA parameters in the init.ora, including all parameter like sort%.
Once the pga_aggregate_target has been set oracle will automatically manage PGA memeory allocation, based upon the individual needs
It can be dynamically changed by alter system command.
There are some workarea_% parametee which can be used in conjuction with the pga_aggregate_target.
Total Unix Ram=fixed sga+ pga + ram reserved for OS