The tub file was a technique used in the punched card era to speed generation of data files. Multiple copies of frequently used cards were prepunched and stored in trays with index tabs between card sets, arranged so that cards would be easy to find. For example, a wholesaler might have a tub file with cards for frequent customers and for each inventory item. Instead of keypunching a set of cards for each purchase order, a clerk would pull out a customer card and then a card for each item that customer ordered. The resulting deck could then be run through a tabulating machine to produce an invoice. This technique was an early form of random access memory and was the initial inspiration for the invention of the hard disk at IBM's San Jose Laboratory, what eventually became the IBM 305 RAMAC.
- Crosby, Kip; Elbaum, Max (April–June 1994). "Just Like the Golden Gate Bridge: Rey Johnson and Jack Harker talk about RAMAC". The Analytical Engine. 1 (4): 4–5. ISSN 1071-6351. Archived from the original on 2007-04-07. Retrieved 2007-06-22.
- Anderson, Arthur O. (2001). "Reynold B. Johnson: 1906–1998". Memorial Tributes: National Academy of Engineering. National Academy Press. 9: 141. ISBN 0-309-07411-8. ISSN 1075-8844. Retrieved 2007-06-22.
- RAMAC Oral History Project, Computer History Museum, at 26:21
- Photo of a tub file at Computer History Museum web site
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