deletion of records in (logntime this is quite fast and works even for very large files howeverthe programming is not trivial hashing if it' acceptable to use about twice as much external storage as file would normally takethen external hashing might be good choice it has the same access time as indexed fileso( )but can handle larger files figure showsrather impressionisticallythese choices for external storage structures start speed important no sequential search yes speed critical no -tree yes extra storage available yes external hashing no indexed files figure relationship of external storage choices virtual memory sometimes you can let your operating system' virtual memory capabilities (if it has themsolve disk access problems with little programming effort on your part if you read file that' too big to fit in main memorythe virtual memory system will read in that part of the file that fits and store the rest on the disk as you access different parts of the filethey will be read from the disk automatically and placed in memory