"The hardware and software is like a car," says Saxena. "It's obviously not enough just to have a car; you need petrol -- the stored information - and you need a driver -- the expert who teaches the machine. I say [implementation] comes in three phases -- build Watson, teach Watson, run Watson."

The initial client for Watson's medical application is US insurance company WellPoint. In the front of the queue on the financial services side is Citibank, a long-term partner of IBM.

And there is a queue of other potential customers, Saxena says. "I feel like I'm having to put my shoulder to the door sometimes, to keep out the crowds saying 'we need a Watson'."

Watson at present has knowledge in the cancer diagnosis and treatment field equivalent to a first-year medical student, he says. It still needs the years of practical experience that student will go through before being allowed to treat patients unaided. Not that Watson will ever be allowed to do that in Saxena's vision.

"It will never replace the doctors; I see it as a decision support system for them.