manhattan phone book. watson can now hold 12 million of them. in the 80s ibm s first pc could understand about 5,000 words. watson, 125 billion. sometimes that data misses the human subtlety. stylish elegance or students who graduated in the same year. watson. what is cheek? no, sorry. reporter: what is class? class, you got it. reporter: the mere mortal got it right. sometimes watson just isn t fast enough. can t sift through all that data. the man who helped build him. watson got the answer but slower. and couldn t buzz in fast enough to reporter: what are you saying behind the scenes? come on? well, of course. let s meet our contestants. reporter: brad rutter, who won the most money ever on jeopardy! now tied with watson. when you first saw that a supercomputer opened up that lead, what were you thinking? i was thinking, wow, okay. this thing s pretty good.