Components of SGA are :

1> Shared pool : consists of shared sql area and shared pl/sql area

2> Data Base buffer cache(DB cache) : contains most recently used blocks & dirty blocks(modified but not yet written to datafile)

3> Redolog Buffer : contains changed/redo data

4> Large pool : used only in parellel sever environment

5> Java pool : used when you are using java strored procedures etc.