SGA size calculation

Hi,

Find the output of the following query.

SQL> select * from v$sga;
NAME VALUE
-------------------- ----------
Fixed Size 744408
Variable Size 922746880
Database Buffers 2013265920
Redo Buffers 3420160

1. Could anyone explain me,what are the oracle memory components comes under "Fixed/Variable/Database Buffers/Redo Buffers" size calculation?

2. Does the sum of these 4 values give the total size of SGA?

Thanks...

just do show sga and it will answer your questions