The databases of any organization typically require a large amount of storage space to store their daily operational information. Corporate company’s database sizes are usually of gigabytes of data or sometimes for largest companies these databases will be of terabytes of data. 1 gigabyte is 1000 megabytes (1 Billion bytes), and 1 terabyte is 1 million megabytes (1 trillion bytes). Since the main memory of computers cannot store this much information, the information is stored on hard disks. Data are moved between disks storage and main memory as needed. Since the movement of data to and from hard disk is slow relative to the speed of the central processing unit, it is imperative that the database system structure the data so as to minimize the need to move between disk and main memory.
The goal of database system is to simplify and facilitate access to data. High-level views help to achieve this goal. Users of the system should not be burdened unnecessarily with the physical details of the implementation of the system.
A storage manager is a program module that provides the interface between the two-level data stored in the database and the application programs and queries submitted to the system. The storage manager is responsible for the interaction with the file manager.