As discussed in the preceding chapters, the goal of a database system is to simplify and facilitate access to data. The users of the system should not be burdened with the physical details of the implementation of the system. Databases are stored physically on storage devices and organised as files and records. The overall performance of a database system is determined by the physical database organisation. Therefore, it is important that the physical organisation of data is efficiently managed.
All data that is processed by a computer cannot reside in the main memory because of the fact that: