Magnetic tape and other magnetic media came to be used as I/O media following paper tape and paper cards, and companies developed auxiliary memory devices that relied on magnetic media. Magnetic tape was initially used in inexpensive external memory devices, and half-inch open reels were the early standard magnetic tape format. With the development and growth of magnetic drums and magnetic disks, magnetic tape became primarily used as a storage media and smaller cartridge formats were introduced to reduce the size of the units．
Magnetic tape was an important storage media for programs and data on early computers. Consequently, the development of magnetic tape units was particularly important, even more so than other peripheral devices. Magnetic tape units were essential in business processes for handling and classifying large volumes of data. Through a joint research project made possible by a grant from the Ministry of International Trade and Industry in 1957, NEC led the development and prototyping of a 10-track vacuum-column magnetic tape unit that had a tape speed of 2 meters per second and a recording density of 4 bits per millimeter. In 1959, NEC completed the commercial 542 magnetic tape unit, which had 8 tracks. Tokyo Shibaura Electric (now Toshiba) also began researching and prototyping magnetic tape units early on and produced an 8-track unit with a tension arm mechanism, a tape speed of 1.5 meters per second, and a recording density of between 4 and 6 bits per millimeter. In 1959, the company completed a magnetic tape verifier, the TOSBAC 4100. NEC, in 1960, built a magnetic tape classifier (with sort and merge functions) by connecting a magnetic tape unit to the NEAC-2203. Several companies also started developing 7-track and 8-track magnetic tape units, with Fujitsu completing the FACOM 601 in 1960, Oki Electric completing the OKITAC-5099 in 1961, and Hitachi completing the H-144 in 1962．
Concurrent with the announcement of its System/360 in 1964, IBM developed a 9-track magnetic tape unit with a recording density of 800 bits per inch. Later, the company boosted the recording density to 1,600 bits per inch, and by 1973 its product had a recording density of 6,250 bits per inch and could store 125 megabytes on a 2,400-foot reel. Fujitsu, Hitachi, and NEC developed units compatible with this media and sold their units as OEM products in overseas markets in the second half of the 1970s. Open-reel magnetic tape was widely used and continued in production until 2001.
As the number of accumulated magnetic tapes soared in the 1970s, it became increasingly difficult to manually change and store magnetic tapes. To overcome these problems, IBM developed the 3850 Mass Storage System (MSS) in 1975. MSS stored cylindrical magnetic-tape cartridges in hexagonal storage bins and used a rotating drive head with a helical scan recording method. A robot moved the cartridges in and out of the read station, allowing the unit to be completely automatic and store several hundred gigabytes. In Japan, NEC and NPL (a joint venture of Hitachi and Fujitsu), in cooperation with Nippon Telegraph and Telephone Public Corporation, developed a similar unit in 1979, leading to Hitachi announcing the H-8523 and NEC announcing the N7651. Fujitsu completed the FACOM 6450 in 1980. Later, Hitachi, NEC, and Fujitsu would abandon the 3850 format and develop tape library units that stored several thousand reels. The largest of these, appearing at the end of the 1990s, could store as much as 100 terabytes．
Demand for inexpensive magnetic tape drives for minicomputers and personal computers grew starting from the 1970s, and tape units with progressively smaller tape widths — from 1/2 inch to 8 millimeter, 1/4 inch, and 1/8 inch — were built．
In 1985, the cartridge-based IBM 3840 (with a capacity of 200 megabytes) began being shipped as a replacement for open-reel units. It eventually became the standard media for mainframe computers. Hitachi, Fujitsu, and NEC developed 3840-cartridge compatible units as well．