concept of operation systems: memory, processes, drivers, file system, services, network communications, application programs, and users environment.
Oracle database series of software products apply grid architecture computing technology, development tools, universal access, security infrastructure and centralized management. Oracle database include Oracle Database, Oracle Application Server, Oracle Enterprise Manager and Oracle Collaboration Suite. The first steps every database lead of area startup database. Oracle database is associates with Oracle instance. In startup Oracle allocates System Global Area (SGA) memory and starts Oracle processes. SGA memory and Oracle processes make Oracle instance. The instance takes control of data and users of database. Along start database Oracle associates instance with the database. This process is named as mount database. Oracle database is in ready status and can be open for users and public activities. Existing users can work with database. Oracle database start and of course shut down is restricted to users who connect to Oracle. Operation system privilege of user allow connect to Oracle with administration privileges or user have assign privileges SYSDBA and SYSOPER. A connect to database with SYSDBA privileges support that owner schema is SYS.
When instance start, Oracle reads SPFILE (server parameter file) or initialization parameter file to make out values of initialization parameters. After Oracle allocates shared memory for use database information and creates background processes. Mount database is realized assist in instance. This database is associated with instance. Instance must find and open database control files. Control files are determined in CONTROL_FILES initialization parameter. After Oracle read control files to take names of database datafiles and redo log files. At the conclusion start sequence Oracle opens on-line datafiles and redo log files. Oracle returns error, if any datafiles or redo log files are not present for open database. It is need recovery database and after start database. Opening database do database available for normal operations and users can connect to open database and use information.