Abstract: The disclosure herein relates to information storage systems and input stages for such systems together with a method of operating such systems. The input stage is designed to accept address signals composed of keyword pairs so that each item of information to be stored or retrieved must be identified by pairs of keywords which may be in plain language. For this purpose the input stage is arranged to recognize three distinct symbols, namely keyword characters, a spacer signal identifying the end of the first keyword of a pair and a terminal signal identifying the end of a pair of keywords. The input stage also identifies a final terminal signal which identifies the end of a set of keyword pairs. The address signal is read symbol by symbol to gate means in the input stage which operates to check that the sequence is in the form of a keyword character or characters, a spacer signal, a keyword character or characters and either a keyword pair terminal signal or a set of keyword pair terminal signals.