This can be seen in Enterprise Manager under ‘Server’ -> ‘Memory Advisors’.

Parts of the SGA:

Shared Pool –> library cache (storage for parsed queries)
Large Pool — used for RMAN and when MTS is configured the users’ session data is stored here.
Java Pool
Fixed SGA
Database Buffer Cache (where results of queries are stored)
Redo Log Buffer

When changing from dedicated server to shared (MTS – multithreaded shared server) the Large Pool may need to be increased because the users’s session data, etc is stored in the Large Pool. Also, the PGA (Program Global Area) is used only for stack space in MTS.