These are three levels of database architecture. Internal layer is the first layer which is for the system designers. This layer deals with the physical storage of data and this layer is used by database system programmers. Structuring of records, Indexing and ordering of records is carried out in this layer. Conceptual layer is the layer for database designers and administrators. This layer deals with the organization of data as a whole. In this layer for removing the unnecessary details of the internal data abstractions are used. Third type of layer External layer that is used by end users and the application programmers. In this layer data is presented in a useful form and parts of data can be hidden.
