IT is now official. Bill has left the building.

There might be small pockets of DR-DOS, OS/2, Netware, Apple and Linux devotees singing “Ding Dong the witch is dead” around the world. But at the Redmond headquarters of Microsoft, where Bill Gates bid farewell to the company he founded with Paul Allen in 1975, it was all tears and reminiscing.

And it’s a little early for the Ding Dong crowd to start singing anyway.

While pulling out of full-time work at Microsoft, he remains chairman, and says he will be involved in the occasional project.

And, he said at his farewell, “there won't be a day in my life that I'm not thinking about Microsoft and the great things that it's doing and wanting to help.”

Now the world’s third richest man, Gates wants to focus on his philanthropy through the Bill and Melinda Gates Foundation.

Both Gates and his former Harvard classmate (and current Microsoft CEO) Steve Ballmer were in tears at the formal goodbye in front of 850 employees on the company’s Redmond campus.

The two went through a history of battles and stoushes the company has had over the years, with the standout being the Microsoft launch of Windows, up against the much bigger IBM.

Gates says he is looking forward to his new roles, which will see him using three separate offices – one at Microsoft in Redmond, one at the Foundation in Seattle’s CBD, and one to pursue personal interests somewhere in between.

Gates says he is most looking forward to the work at the Foundation, saying he is glad that he’ll have nothing to do with the hands-on running of the organisation, but rather will engage in “strategy and advocacy” work.