Early electronic computers such as Colossus made use of
punched tape, a long strip of paper on which data was
represented by a series of holes, a technology now obsolete.
Electronic data storage, which is used in modern computers,
dates from World War II, when a form of delay-line memory was
developed to remove the clutter from radar signals, the first
practical application of which was the mercury delay line. The
first random-access digital storage device was the Williams tube,
based on a standard cathode ray tube, but the information stored
in it was volatile in that it had to be continuously refreshed, and
thus was lost once power was removed. The earliest form of nonvolatile computer storage was the magnetic drum, invented in
1932 and used in the Ferranti Mark 1, the world’s first
commercially available general-purpose electronic computer.
Information Technology. Internet: <en.wikipedia.org> (adapted).