The major advancement presented by the phototypesetting machines over the Linotype machine hot-type machines was the elimination of metal type, an intermediate step no longer required once offset printing became the norm. This cold-type technology could also be used in office environments where hot-metal machines (the Mergenthaler Linotype, the Harris Intertype and the Monotype) could not. The use of phototypesetting grew rapidly in the 1960s when software was developed to convert marked up copy, usually typed on paper tape, to the codes that controlled the phototypesetters.