The Selectron was a competitor to the Williams tube designed by RCA. It was supposed to have a capacity of 4096 bits but production had stalled by 1948. RCA aimed lower with a model with 256-bit capacity, but it only ever ended up in use with one computer. The Selectron was a long vacuum tube with a heated cathode inside. Radial and axial wires surrounded the cathode in a grid formation with four segments. Using the same “secondary emission” principle involving positively and negatively charged areas as the Williams tube, the Selectron stored bits on signal plates. This technology was faster and more reliable than the Williams tube, but far trickier to produce.