The physical model operates at the lowest level of abstraction, describing the way data are saved on storage media such as disks or tapes. The physical model requires the definition of both the physical storage devices and the (physical) access methods required to reach the data within those storage devices, making it both software- and hardware dependent. The storage structures used are dependent on the software (the DBMS and the operating system) and on the type of storage devices that the computer can handle. The precision required in the physical model’s definition demands that database designers who work at this level have a detailed knowledge of the hardware and software used to implement the database design.
Although the relational model does not require the designer to be concerned about the data’s physical storage characteristics, the implementation of a relational model may require physical-level fine-tuning for increased performance. Fine-tuning is especially important when very large databases are installed in a mainframe environment. Yet even such performance fine-tuning at the physical level does not require knowledge of physical data storage characteristics.