External
storage (also called auxillary storage) is any storage other than
main memory. In modern times this is mostly hard drives and removeable media
(such as floppy disks, Zip disks, optical media, etc.). With the advent of USB
and FireWire hard drives, the line between permanent hard drives and removeable
media is blurred. Other kinds of external storage include tape drives, drum
drives, paper tape, and punched cards. Random access or indexed access devices
(such as hard drives, removeable media, and drum drives) provide an extension
of memory (although usually accessed through logical file systems). Sequential
access devices (such as tape drives, paper tape punch/readers, or dumb
terminals) provide for off-line storage of large amounts of information (or
back ups of data) and are often called I/O devices (for input/output).