Deciding to enter the console market with the original Xbox one month after becoming Microsoft CEO was "my decision, my accountability," Steve Ballmer told Fortune.

Ballmer, who will step down as CEO sometime in 2014, saw the decision, in part, as a way to assert himself in his new role.

"I believe in accountability," Ballmer said. "I'm in. I'm accountable. I'll make this work — not that I had to drive it — but we had some bumps on the road. And it was important that I stay accountable, stay patient, and stay behind the decision that we made."

Robbie Bach, Microsoft's former president of Entertainment and Devices, recalled that Ballmer spent six months researching before giving Xbox the greenlight.

"He was willing to step out into a space that Microsoft had never been in, look at a business model, and say, 'This is something we need to try,'" Bach said.