chap file processing and external sorting medium ram disk flash drive floppy tape $ figure price comparison table for some writeable electronic data storage media in common use prices are in us dollars/mb primary versus secondary storage computer storage devices are typically classified into primary or main memory and secondary or peripheral storage primary memory usually refers to random access memory (ram)while secondary storage refers to devices such as hard disk drivesremoveable "flashdrivesfloppy diskscdsdvdsand tape drives primary memory also includes registerscacheand video memoriesbut we will ignore them for this discussion because their existence does not affect the principal differences between primary and secondary memory along with faster cpuevery new model of computer seems to come with more main memory as memory size continues to increaseis it possible that relatively slow disk storage will be unnecessaryprobably notbecause the desire to store and process larger files grows at least as fast as main memory size prices for both main memory and peripheral storage devices have dropped dramatically in recent yearsas demonstrated by figure howeverthe cost for disk drive storage per megabyte is about two orders of magnitude less than ram and has been for many years there is now wide range of removable media available for transferring data or storing data offline in relative safety these include floppy disks (now largely obsolete)writable cds and dvds"flashdrivesand magnetic tape optical storage such as cds and dvds costs roughly half the price of hard disk drive space per megabyteand have become practical for use as backup storage within the past few years tape used to be much cheaper than other mediaand was the preferred means of backup "flashdrives cost the most per megabytebut due to their storage capacity and flexibilityhave now replaced floppy disks as the primary storage device for transferring data between computer when direct network transfer is not available secondary storage devices have at least two other advantages over ram memory perhaps most importantlydisk and tape files are persistentmeaning that