data structures using each cylinder will have an entry corresponding to the largest key value into that cylinder if the disk has usable surfacesthen each of the surface indices will have entries thereforethe ith entry in the surface index for cylinder is the largest key value on the jth track of the ith surface hencethe total number of surface index entries is the physical and logical organization of disk is shown in fig note the number of cylinders in disk is only few hundred and the cylinder index occupies only one track when record with particular key value has to be searchedthen the following steps are performedfirst the cylinder index of the file is read into memory secondthe cylinder index is searched to determine which cylinder holds the desired record for thiseither the binary search technique can be used or the cylinder index can be made to store an array of pointers to the starting of individual key values in either case the search will take (log mtime after the cylinder index is searchedappropriate cylinder is determined depending on the cylinderthe surface index corresponding to the cylinder is then retrieved from the disk since the number of surfaces on disk is very smalllinear search can be used to determine surface index of the record once the cylinder and the surface are determinedthe corresponding track is read and searched for the record with the desired key hencethe total number of disk accesses is three--firstfor accessing the cylinder indexsecond for accessing the surface indexand third for getting the track address howeverif track sizes are very large then it may not be good idea to read the whole track at once in surface such situationswe can also include sector multiple addresses but this would add an extra level tracks of indexing andthereforethe number of one surface cylinder accesses needed to retrieve record will then surface become four in addition to thiswhen the file extends over several disksa disk index surface will also be added surface the cylinder surface indexing method of maintaining file and index is referred surface to as indexed sequential access method sectors (isamthis technique is the most popular and simplest file organization in use for figure physical and logical organization of disk single key values but with files that contain multiple keysit is not possible to use this index organization for the remaining keys multi-level indices in real-world applicationswe have very large files that may contain millions of records for such filesa simple indexing technique will not suffice in such situationwe use multi-level indices to understand this conceptconsider file that has , records if we use simple indexingthen we need an index table that can contain at least , entries to point to , records if