Significance of the setting of the PGA_AGGREGATE_TARGET parameter

Hi,
   My customer has a 2-node RAC database (version 11.2.0.3). The setting of the PGA_AGGREGATE_TARGET is 512Mb on each instance. Some time after the instances were started I looked at the contents of 'V$PGASTAT' and saw the following (both instances showed similar values):


SQL> SELECT * FROM V$PGASTAT;

NAME                                                                  VALUE UNIT

---------------------------------------------------------------- ---------- ------------

aggregate PGA target parameter                                    536870912 bytes

aggregate PGA auto target                                          33554432 bytes

global memory bound                                               104857600 bytes

total PGA inuse                                                  6338245632 bytes

total PGA allocated                                              7810515968 bytes

maximum PGA allocated                                            7956495360 bytes

total freeable PGA memory                                         970719232 bytes

process count                                                          1089

max processes count                                                    1099

PGA memory freed back to OS                                      2.3735E+11 bytes