Database and Instance Startup and Shutdown

Every running Oracle database is associated with an Oracle instance. When a database is started on a database server (regardless of the type of computer), Oracle allocates a memory area called the System Global Area (SGA) and starts one or more Oracle processes. This combination of the SGA and the Oracle processes is called an Oracle Instance. The memory and processes of an instance manage the associated database's data efficiently and serve the one or multiple users of the database.