Digital Differential Analyzer

a special-purpose digital integrating machine based on digital integrators that integrate with respect to an independent variable presented in the form of increments in either the binary or ternary number system.

Problems are solved in a digital differential analyzer through the interaction of integrators arranged in much the same way as in the problem composition circuits in an analog computer. The digital differential analyzer occupies an intermediate position between analog and digital computers. With respect to preparation and problem-solving methods, digital differential analyzers have much in common with analog computers, but with respect to data representation and the elements used they are similar to the digital computer.

Digital differential analyzers can compute more accurately than analog computers but are slower and less flexible; they can integrate with respect to any independent variable, whereas analog computers can integrate only with respect to time. Digital differential analyzers, unlike digital computers, cannot solve complex logical problems.

Since the change of variables in digital differential analyzers is determined by the accumulation of increments, the speed of a digital differential analyzer is inversely proportional to the degree of precision provided. As the required precision is increased, the magnitude of each elementary increment must be smaller, and the speed correspondingly decreases.

A distinction is made between sequential and parallel digital differential analyzers. In sequential analyzers, integration is performed by repeated use of a single physical integrator and by storage of the result of integration. Analyzers of this type are relatively simple and inexpensive. In parallel analyzers, all of the integrators operate simultaneously. Analyzers of this type are more complex and expensive than those of the sequential type, but they are faster.