The standard in the 21st century is for computers to come equipped with a certain amount of storage on their hard drives. Typical sizes are 160 GB (gigabytes), 250 GB, or 500 GB. By the standards of the original disk drives in 1956 that could hold 5 megabytes (MB), these are gigantic. The size of applications and certain types of files, such as multimedia files, however, means that even these large hard drives can fill up quickly. In addition, there is often a need for back up for the sake of security. For these reasons, external storage solutions, sometimes referred to as secondary storage devices, are often used.
Over the years, a range of secondary storage devices have been devised and used. Some are much less popular in the present, including vacuum tubes, punch cards and punch tape, magnetic drums. Floppy disks, also called diskettes, both 5 1/4 inches (13.335 cm) and 3 and 1/2 inches (8.89 cm) came and went in the 20th century. Zip disks, which are similar in dimensions to the smaller floppies, survive, and hold between 100 and 750 MB of data, as does the REV disk, which holds up to 90 GB of data. Magnetic tape endures as a storage device, having been used for over 50 years.
Various types of CDs and DVDs are commonly used secondary storage devices. Both of these are types of optical discs, written and read by means of light. They are three types. Read-only examples include CDs, CD-ROMS, DVD-ROMS, and DVD-Videos. Write Once Read Many (WORM) examples include CR-Rs, DVD-Rs, DVD+Rs, and WORMs. Finally, optical secondary storage devices include CD-RWs, DVD-RAMS, DVD-RWs, DVD+RWs, and MOs.
Other storage devices include external hard drives. These may be mobile or desktop models. Some are made not only for storage but also for streaming music, movies, or photos, to multimedia devices like Xbox 360® or PlayStation® 3.
USB Flash drives come in many models and hold from 512 MB to 256 GB, the storage capacity of the Kingston® DataTraveler® 300, which the manufacturer claims is the world’s largest USB Flash drive. These secondary storage devices are also known as flash drives, pen drives, thumb drives, and by other names. Many USB Flash drives are meant to be attached to a key ring or worn around the neck on a lanyard.