Sequential organization: This requires that to retrieve a specific record, all proceeding records are scanned and passed over. The advantage of a sequential organization is rapid access to the next record which constitutes both the physical as well as the logical record in the file but its disadvantage is that it is difficult to update. Typical examples of sequentially organized files can occur on serial etc. However, file on direct access storage media can be efficiently organized sequentially too.
Random organization: This ignores the physical sequence of the records stored and records are accessed on the basis of their physical location (not in any sequence anyway) on the storage medium. the advantage of a random organization is that any record in a collection can be reached without scanning all preceding records. This form of organization applies to most files on direct access storage media such as magnetic disks and drums. Records are identified and located by a hashing function technique or by specifying the relative record number.
Indexed organization: This requires an index to be created. This index consists of a collection of entries; each entry corresponds to data record and contains the value of a key attribute for that record and a pointer which allows immediate access to that record. The index may be part of the file or may be separate file.
Indexed sequential file organization: This is similar to a sequential file organization in that rapid sequential processing is possible, even though the file must be resident on a direct access storage medium. Similarly, non-sequential processing is very possible for an indexed sequential file. In ordinary indexed organization, only non-sequential processing is usually done on the data records.
