Communications Technology Handbook, 2nd Edition

19 Memories

A memory element is a multi-state device that has the ability to retain its present state until forced to change by an input of energy. In communications applications, a memory consists of a group of cells, each of which is capable of taking up one of two states. A memory is thus a binary device. In general, memories fall into one of three categories, depending upon the nature of the stored energy. Magnetic stores are used chiefly as secondary or backing stores, while optical memories, which are a comparatively new concept, are used mostly for archiving purposes. The major devices used for communications purposes are based on semiconductor technology. A memory that loses its stored data when the power is removed is described as being ...