Outgoing Microsoft CEO Steve Ballmer has revealed that Vista was his biggest regret during his 33-year career with the company, Digital Spy said.

Speaking to ZDnet, the 57-year old admitted that he had "had a chance to make a lot of mistakes".

"I would say probably the thing I regret most is the, what shall I call it, the loopedy-loo that we did that was sort of Longhorn to Vista," Ballmer said.

He went on to say that Microsoft 'birthed' computing in the '80s and '90s, naming it as his proudest moment.

"I'm proud of being I would say a significant part even of the birth of intelligent personal computing, the notion that people use computing technologies, whether that's phones, PCs," he said.

"I would say a billion plus people and now more with phones, even if they're not all our phones, I'm very proud of what we've accomplished there."

Ballmer revealed that he only made his final decision two days before announcing his retirement publicly on Friday (August 23).

"I've thought about it for a long time, but the timing became more clear to me over the course of the last few months," he said.

"We worked hard on our strategy process, our org process. And frankly I had no time to think about it during all of that... I would say my thinking has intensified really over the last couple, two, two and a half months, something like that."

The CEO added that Bill Gates "respected" his decision and that he has no immediate plans for the future.