It was really phenomenal [Warren Buffett donation]. It grew out of the friendship that we had and the fact that his plan to have his wife run the foundation and give things away changed when she tragically died.

Windows is probably the most important product in the entire PC industry. Everything we do in terms of supporting touch, new hardware, accessibility has incredible impact.

It's the poorer people in tropical zones who will get really hit by climate change - as well as some ecosystems, which nobody wants to see disappear.

Taking a look back, one big reqret is, I left Harvard with no real awareness of the awful inequities in the world. The appalling disparities of health and wealth and opportunity that condemned millions of people to the lives of despair. I learned a lot here at Harvard about new ideas and economics, and politics. I got great exposure to the advances being made in the sciences. But humanities greatest advances are not in its discoveries, but in how those discoveries are applied to reduce inequity.

The 'Billionaire' song is what my kids tease me with. They sing it to me. It's funny.

I'm an investor in a number of biotech companies, partly because of my incredible enthusiasm for the great innovations they will bring.

Like a human being, a company has to have an internal communication mechanism, a "nervous system", to coordinate its actions.