| An Oracle database comprises an instance and data storage. The instance comprises a set of operating system processes and memory structures that interact with the storage. Processes can in turn archive the online redo logs into archive logs (offline redo logs), which provide the basis (if necessary) for data recovery and for some forms of data replication.
The Oracle RDBMS stores data logically in the form of tablespaces and physically in the form of data files. Tablespaces can contain various types of segments, for example, Data Segments, Index Segments etc. Segments in turn comprise one or more extents. Extents comprise groups of contiguous data blocks. Data blocks form the basic units of data storage. At the physical level, data files comprise one or more data blocks.
Oracle keeps track of its data storage with the help of information stored in the SYSTEM tablespace. The SYSTEM tablespace contains the data dictionary - and often (by default) indexes and clusters.
The Oracle DBMS can store and execute stored procedures and functions within itself. Such code can operate under PL/SQL (Oracle Corporation's proprietary procedural extension to SQL), or under the object-oriented language Java.
In , Oracle Corporation released Oracle Database 10g. The g stands for "grid"; emphasizing a marketing thrust of presenting 10g as "grid-computing ready".
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