CAM Hardware

Abstract

In this chapter, several detailed circuits and physical principles for the implementation of CAM functions are presented. It may be necessary to point out that not all of them have been used in practice; it is quite possible that certain solutions, although patented, may not prove practicable. It may be said definitely that semiconductor CAM circuits which are based on approved logic switching principles have already established their status in computer technology. Magnetic elements, although sometimes extensively studied, must now be considered obsolete. An important exception are the magnetic-bubble memories which are beginning to replace disk memories; it seems possible to add active searching and sorting functions to them. The oldest cryotronic principles, although once extensively studied, too, can no longer compete with LSI semiconductor circuits in packing density. On the other hand, the most modern superconducting switches, the Josephson junction devices, have the highest packing density of all known electronic switches, and they are seriously considered for ultra-high-speed computers. These devices have already been applied to buffer memories, although they too are still at an experimental stage of development. Finally, the optical, especially holographic memories ought to be mentioned. The general trend has for some time been away from them since comparable packing densities are achievable by LSI circuits.