Would you buy a DVD or CD player that had one disk sealed inside? Of course not. You expect to use a DVD or CD player with many relatively inexpensive disks. On a computer as well, using many inexpensive cartridges with one drive lowers the overall cost. Low cost is the defining characteristic of tertiary storage, which we discuss in this section.

Because cost is so important, in practice, tertiary storage is built with removable media. The most common examples are floppy disks, tapes, and read-only, write-once, and rewritable CDs and DVDs. Many any other kinds of tertiary-storage devices are available as well, including removable devices that store data in flash memory and interact with the computer system via a USB interface.