CORE RANDOM ACCESS MEMORY (RAM)
cores were used as the primary memory of early mainframe computers. Each data bit was stored as the magnetic polarity of a tiny bead of ferrite called a core. The beads were strung by hand at the intersection of three wires. A core plane was composed of hundreds of fine copper wires in a mesh finer than window screen (pictured at right). Although this type of memory is no longer used in general purpose computers, it is used extensively in "hardened" military and aerospace applications because it is impervious to radiation and the electromagnetic pulse associated with nuclear detonations.

Wang main program board. Closeup.