Magnetic-core memory was the predominant form of memory for 20 years (circa 1955–75). It uses tiny magnetic toroids (rings), the cores, through which wires are threaded to write and read information. The products in the 50's were hand made, sometimes utilising the handiwork of people leaving the cotton industry that was in decline in the UK who had comparative skills. See at the National Museum of Computing (www.tnmoc.org). See their other highlights on their iPhone app (search TNMOC).