This article is from the storage FAQ part1, by Rodney D. Van Meter with numerous contributions by others.
Quarter Inch Cartridge. Primarily low-end (ie, PC) available from multiple vendors but 3M is pushing it into midrange market with estimates of 100 Gigabytes per cartridge by 1999. Two-reel cassette. In Dec '94, 3M, Sony, HP and others announced a new format, 2.3 times the capacity, available mid-1995. The cartridge and drive mechanics apparently change. It will be .315 inch tape instead of .25, with 750 feet of media in a cartridge. (rdv, 94/12/16)