 The IBM 7340 Hypertape drive, introduced in 1961, used a dual reel cassette with a wide tape capable of holding 2 million six-bit characters per cassette.In the 1970s and 1980s, audio Compact Cassettes were frequently used as an inexpensive data storage system for home computers, or in some cases for diagnostics or boot code for larger systems such as the Burroughs B1700.Compact cassettes were logically, as well as physically, sequential; they had to be rewound and read from the start to load data.