5. A system as in claim 4 in which each group of comparison means comprises a plurality of sub-groups of comparison logic each comprising: first register means for storing said data word; second register means for storing a file word; and comparing means responsive to said stored data word and said stored file word to generate one of said comparison indicating signals.
4. A system for determining with which of a plurality of groups of file words a data word most closely compares and comprising: a plurality of groups of comparison means each constructed to simultaneously compare each file word of each group of file words with said data word to produce a comparison indicating signal for each comparison of said data word with a file word; means for identifying each group of file words in which the comparison of not more than one file word with the data word produces a comparison indicating signal whose amplitude exceeds, in a given polarity direction, a particular threshold level, and for identifying each of said one file words; and means responsive to the comparison indicating signals from each group of file words to establish such particular threshold level.