In the 1970s, speech recognition worked by brute force, trying to match each word individually, one at a time; in the 1980s most researchers adopted a mathematical technique developed at Princeton in the 1960s, called Hidden Markov Modeling, that worked out the probability that a sound was a specific word. 1982 saw the launch of three major companies; Covox, Dragon Systems and Kurzweil. By the mid-1980s or 1990s they all had voice recognition software that ran on a PC rather a mainframe, as did IBM, but it was still only able to handle a few words at a time. Kurzweil could recognize 1,000 words in 1985 and 20,000 words in 1987 but it was 1995 before it was right more than half the time. And software was pricey; in 1990 DragonDictate cost $9,000.