Virginia M. Rometty, the chief executive and newly appointed chairman of I.B.M., answered a mysterious and pressing question on Tuesday: Where is Watson?

Watson is the room-size computer that defeated its human rivals to become a “Jeopardy!” champion. The answer, Ms. Rometty said at Fortune’s Most Powerful Women summit, is that Watson is in medical school.

The computer is working with many health care organizations to learn medical data so it can diagnose cancer, and that is just the beginning. It has so far ingested 80 percent of the world’s medical data.

“Watch it work, and it’s almost as if he’s talking to a colleague,” Ms. Rometty said. “The beauty of it is it tells you what’s right or wrong,” and explains with confidence why it believes what it says.

Watson’s skills – from “Jeopardy!” to oncology to working with banks and call centers – are part of I.B.M.’s bigger aim. It is called cognitive computing, which she described as machines that can learn.

“In this world of huge and big data, you won’t be able to program machines for everything they should know,” said Ms. Rometty. “These machines will have to learn what is right, what is wrong, what is a pattern.”

It is the third wave of computing, she said. At first, computers could count. Today, they are programmed to follow “if this, then that.” Next they will need to discover and learn on their own, she said, not just as a search engine, but proactively. The next era, for all jobs, not just those in computing, will be to help businesses sift big data, she said.

“It’s going to be a whole era to help you get through this, and everyone’s job, from chief marketing officer to chief of police, their jobs are going to be redefined by that,” she said.