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Oracle stores data logically in the form of ''tablespaces'' and physically in the form of ''data files''. Tablespaces are conceived based on the type of the data ''segments'' they contain, for e.g., Data Segments, Index Segments, Bootstrap Segments, etc. Segments in turn are made up of one or more ''extents''. Extents are grouped based on contiguous ''data blocks''. Data blocks are the basic unit of data storage. At the physical level, data files are made up of one or more data blocks, where the blocksize can be variable.
Oracle keeps track of data storage with the help of information stored in the ''System'' tablespace. The System tablespace contains the ''Data Dictionary'', indexes and clusters. Data dictionary is a special collection of tables that contains information about all user objects in the database.
An Oracle database installation traditionally comes with a default [[schema]] called ''scott''. After the sample tables have been created, the user can log into the database with the user ''scott'' and password ''tiger''. These names come from [[Bruce Scott]] who was one of the first employees at Oracle (then Software Development Laboratories). Tiger was the name of his cat.
==History==
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