Data storage and retrieval systems

Claim 1

A process for retrieving, from a file of information items each identified by an index number, the index number of each item for which a desired value obtains for each of a predetermined number of retrieval criteria, the process comprising: forming a magnetically recorded index tape separate from the file of information items by, for each information item, carrying out the steps of: providing a criteria recorder having a plurality of recording positions each capable of recording only a single bit by being either set or unset, each recording position corresponding to a value of a retrieval criterion, and there being for each retrieval criterion a plurality of recording positions each corresponding to a different alternative value of that criterion, entering the value of each retrieval criterion which obtains for the item by causing only each recording position which corresponds to such a value to be set and the remainder to be unset, reading the settings of the recording positions to generate a string of binary electrical signals each representing the setting of a different recording position, and magnetically recording the said string serially on the said index tape together with the index number of the information item; entering each retrieval-criterion value that it is desired should obtain for an item to be retrieved into an electronic register having plurality of binary stages each corresponding to a different retrieval-criterion value, by causing each stage which corresponds to a desired retrieval-condition value to be set, the remainder being unset; reading the tape to obtain, for each information item, the said recorded string of binary electric signals and index number, outputting the contents of the aid register as a plurality of binary electrical signals each representing the setting of a different one of the said stages; comparing each binary signal of the said string with the binary signal representing the corresponding stage of the said register; and displaying the index number of each item for which a predetermined number of signals representing set stages in the said register match the corresponding signals in the said string, thereby displaying the index number of each informtion item for which a desired value obtains for each of a predetermined number of retrieval criteria.