What Is Sequential File Organization?

In sequential file organization records are arranged in physical sequence by the value of some field, called the sequence field. Often the field chosen is a key field, one with unique values that are used to identify records. The records are simply laid out on the storage devices, often magnetic tape, in increasing or decreasing order by the value of the sequence field.

For example IBM's sequential Access Method SAM among others, uses this organization. This organization is simple, easy to understand and easy to manage but is best for providing sequential access, retrieving records on faster another in the same order in which they are stored. It is not good for direct or random access, which means picking out a particular record; because it generally requires that we pass over prior records in order to find the target record.

It is also not possible to insert a new record in the middle of the file. Sequential is the oldest type of file organization and despite its shortcomings is well suited for certain applications. In sequential file organization records arranged like in physical positions. Retrieving records take much time.

We can physically order the records of a file on disk based on the values of one of their fields called the ordering field. This leads to an ordered or sequential file. Records are placed in an order in sequential file and that's why it is totally different from unordered files where records are stored in the order in which they are inserted, it means that if new records are inserted then they took place at the end of file.Sequential files have many advantages as given below.

* To find a record in the sequential file is very efficient, because all files are stored in an order and no sorting is required.
* Finding the next record from a current record is also very efficient and it does not require additional block access as the next record is in the current record.
* If we use a technique like Binary Search, then it becomes more efficient and easy to search a record. While on the other hand if we search a record in an unordered file then we have to check the whole file because records are stored in no order in unordered file. Sequential files are also known as Sorted files.

It is a method of organizing stored or saved files on a secondary storage device.in this method records are sequentially organized in a file & stored one after another, the sequence is usually based upon a key field.these records must also be retrieved sequentially for processing.