ORACLE INSTANCE

Single Instance systems.

An oracle database server consists of an Oracle database and an orcale instance.Every time database is started a system global area (SGA) is allocated and oracle background processes are started. The combination of the background processes and memory buffers is called an oracle instance.

Every running Oracle database is associated with an oracle instance. When a database is started on a databse 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 process of an instance manage the associated databases data efficiently and serve the one or multiple users of the database.