the data indexed sequential files can be stored only on devices that support random accessfor examplemagnetic disks for exampletake an example of college where the details of students are stored in an indexed sequential file this file can be accessed in two wayssequentially--to print the aggregate marks obtained by each student in particular course or randomly--to modify the name of particular student table summarizes the featuresadvantagesand disadvantages of indexed sequential file organization table indexed sequential file organization features advantages disadvantages provides fast data retrieval records are of fixed length index table stores the address of the records in the file the ith entry in the index table points to the ith record of the file while the index table is read sequentially to find the address of the desired recorda direct access is made to the address of the specified record in order to access it randomly indexed sequential files perform well in situations where sequential access as well as random access is made to the data the key improvement is that the indices are small and can be searched quicklyallowing the database to access only the records it needs supports applications that require both batch and interactive processing records can be accessed sequentially as well as randomly updates the records in the same file indexed sequential files can be stored only on disks needs extra space and overhead to store indices handling these files is more complicated than handling sequential files supports only fixed length records indexing an index for file can be compared with catalogue in library like library has card catalogues based on authorssubjectsor titlesa file can also have one or more indices indexed sequential files are very efficient to usebut in real-world applicationsthese files are very large and single file may contain millions of records thereforein such situationswe require more sophisticated indexing technique there are several indexing techniques and each technique works well for particular application for particular situation at handwe analyse the indexing technique based on factors such as access typeaccess timeinsertion timedeletion timeand space overhead involved there are two kinds of indicesordered indices that are sorted based on one or more key values hash indices that are based on the values generated by applying hash function ordered indices indices are used to provide fast random access to records as stated abovea file may have multiple indices based on different key fields an index of file may be primary index or secondary index primary index in sequentially ordered filethe index whose search key specifies the sequential order of the file is defined as the primary index for examplesuppose records of students are stored in student file in sequential order starting from roll number to roll number nowif we want to search