Semipermanent memory using capacitor charge storage and IGFET read-out

One of the earliest computers used capacitors as its memory.¹ A mechanical means was used for both read-in and read-out operations. Electronic accessing was used in conjunction with vacuum tube or solid-state diodes in relatively modern computers such as the SEAC computer.² Capacitor storage is rarely used at present since magnetic memories meet the modern computer requirements much better. The inherent difficulty with capacitor storage was the limited holding time since a nonlinear resistor with small enough leakage currents to allow useful memory holding time was then not readily available. The old capacitor memory was charged through a diode with slow recovery time and with leakage current of 10⁻¹⁰ amp at best and required a large capacitor for any appreciable holding time. Furthermore, the read-out was usually destructive.