Semipermanent Memory Using Capacitor Charge Storage and IGFET Read-out

One of the earliest computers used capacitors as its memory.1A 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.2Capacitor 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 10−10amp at best and required a large capacitor for any appreciable holding time. Furthermore, the read-out was usually destructive.