There are various limitations of primary memory like limited capacity which is its not enough to store a very large volume of data and volatility which is when power is turned off data stored is lost. So Secondary storage system should provide large storage capacities, low cost per bit as well as medium access times. Magnetic media have been used for these purposes for a long time. Current magnetic data storage devices take form of floppy disks in addition hard disks and are used as secondary storage devices. However audio and video media either in compressed form or uncompressed form need higher storage capacity than other media forms and storage cost for these kinds of media is considerably higher.
Optical storage devices provide a higher storage density at a lower cost. CD-ROM can be used as optical storage device. Many software companies provide both operating system and application software on CD-ROM today. This technology has been main catalyst for development of multimedia in computing since it is used in multimedia external devices like video recorders and digital recorders (Digital Audio Tape) that can be used for multimedia systems.
Removable disk, tape cartridges are other forms of secondary storage devices are used for back-up purposes having higher storage density and higher transfer rate.