Content-Addressable Memories

Designers and users of computer systems have long been aware of the fact that inclusion of some kind of content-addressable or 'associative' functions in the storage and retrieval mechanisms would allow a more effective and straightforward organization of data than with the usual addressed memories, with the result that the computing power would be significantly increased. However, although the basic principles of content-addressing have been known for over twenty years, the hardware content-addressable memories (CAMs) have found their way only to special roles such as small buffer memories and con- trol units. This situation now seems to be changing: Because of the develop- ment of new technologies such as very-large-scale integration of semiconduc- tor circuits, charge-coupled devices, magnetic-bubble memories, and certain devices based on quantum-mechanical effects, an increasing amount of active searching functions can be transferred to memory units. The prices of the more complex memory components which earlier were too high to allow the application of these principles to mass memories will be reduced to a fraction of the to- tal system costs, and this will certainly have a significant impact on the new computer architectures. In order to advance the new memory principles and technologies, more in- formation ought to be made accessible to a common user.