In Figure-1 we can see clearly where the mapping or connectivity is performed between different levels of the database management system. Figure-1 is showing another very important concept that the internal layer and the physical layers lie separately the Physical layer is explicitly used for data storage on disk and is the responsibility of the Operating system. DBMS has almost no concern with the details of the physical level other than that it passes on the data along-with necessary instructions required to the store that data to the operating system.

Figure-2 on the next page shows how data appears on different levels of the database architecture and also at that of physical level. We can clearly see that the data store on the physical level is in binary format and is separate from the internal view of data in location and format. Separation of the physical level from the internal level is of great use in terms of efficiency of storage and data retrieval.

Fig: 2. Representation of data at different levels of data base Architecture and at the physical level at bottom

At the internal level we can see that data is prefixed with Block Header and Record header RH, the Record header is prefixed to every record and the block header is prefixed to a group of records; because the block size is generally larger than the record size, as a result when an application is producing data it is not stored record wise on the disk rather block wise which reduces the number of disk operations and in-turn improves the efficiency of writing process.

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