Open-reel tape
Two exposed reels threaded past the heads by hand — the dominant mainframe storage format from the 1950s into the 1980s.
Half-inch (or quarter-inch) tape on open supply and take-up reels, threaded through the transport by hand. UNIVAC's UNISERVO (1951) was the first commercial tape drive; IBM's 726 followed in 1952. Nine-track half-inch became the interchange standard. The format was fragile and slow to load, and was eventually replaced by sealed cartridges and cassettes (QIC, DLT). Tension arms or vacuum columns kept the tape taut.