The SGA (System Global Area) in Oracle Instance
System Global Area (SGA) memory is memory shared by all server and background processes.
The SGA is made up of three mandatory components and three optional elements.
Mandatory components:
Shared memory area
Database buffer cache
Redo log buffer
Optional items:
LARGE POOL memory area
Java memory area (Java Pool)
Streams memory area (streams pool)
To learn more about the components and basic concepts of the Oracle architecture, take look at our Expert DBA Team Club blog and more advance topics are available at this source.