Internal Level:

The internal or physical level describes the physical storage structures of the database and file organization used to store data on physical storage devices. The internal level describe how the data is stored in the database. It works with operating system and DBMS for storing and retrieving data to and from the storage devices.

Although, both internal level and physical level is considered as a single level, but there is slight difference between them. Actually physical level in one that is managed by the operating system under the direction of DBMS, while the internal level is managed by DBMS.

An internal record is a single stored record. It is storage unit that is passed up to the internal level through stored record interface. The stored record interface is the boundary between physical level and the internal level. This interface is provided to the DBMS by operating system. In some cases, the DBMS itself may create this interface for representing the information. The physical level below this interface consists of database, which is stored and managed by operating system. The operating system creates the physical record interface to access the data of database stored on storage devices that maybe used different purposes.

The internal level is described by means of the internal schema which defines how data is represented, how record are sequenced what indexes exist etc. The internal schema is written in DDL.