Widespread and persistent interest in the impleunit. Typical figures derived from computer simulation mentation of multilevel logic, conditional probability computers, range from 30 to 300 levels.'-3 learning machines, and brain models has created a need for an in-W. . b expensive analog or quasi-digital storage element. A number of possible approaches to this problem, ranging from the slow and the value one level at a time, it is not necessary to be reliable electromechanical systems to the many forms of charge and able to reproduce a given level exactly, as it would be if flux integration, are reviewed, and the suitability of each device for the machine were to perform arithmetic operations. A various fields of application is briefly discussed. way of resetting the value to some arbitrary zero level