Steve Ballmer and Bill Gates have a lot in common. They were both CEOs of Microsoft, they are two of the wealthiest people in the world, and they both dropped out of prestigious universities to work at the computer company founded by Gates and Paul Allen in 1975.

But when Ballmer joined Microsoft in 1980, the company had yet to dominate the personal computer market, eventually creating three billionaires. 

Ballmer recently sat down with Carlyle Group co-founder David Rubenstein to discuss his career.