SEATTLE, June 26 : Sensing the start of a personal computer revolution, Bill Gates dropped out of Harvard in 1975 to start Microsoft Corp and pursue a vision of a computer on every desk and in every home.

Three decades later, Gates is set to step down on Friday from what is now the world’s largest software company to work full-time at the charitable organisation — the Bill & Melinda Gates Foundation — built by his vast fortune.

No longer the world’s richest man — he has been topped by investor Warren Buffett and Mexico’s telecom tycoon Carlos Slim — Gates says great wealth brings with it great responsibility.

The 52-year-old, whose boyish looks seem at odds with his graying hair, will leave behind a life’s work developing software to devote energy to finding new vaccines or to micro-finance projects in the developing world.

As Microsoft’s biggest shareholder, Gates will remain chairman and work on special technology projects. His 8.7 per cent stake in Microsoft is worth about $23 billion.

Gates first programmed a computer at 13, creating a class scheduling system for his Seattle high school. As he gained more experience, he realised the potential that software held to change how humans worked, played and communicated. “When I was 19, I caught sight of the future and based my career on what I saw. I turned out to have been right,” Gates wrote in his 1995 book The Road Ahead.

Gates realised at an early stage of the PC revolution that software would be more important than hardware. Working with boyhood friend Paul Allen, Gates founded Microsoft, naming the company for its mission of providing microcomputer software.

The control panel

Does Gates’ departure leave a vacuum? Here’s a look at the remaining leaders at Microsoft...

Steve Ballmer, 52, Chief Executive Officer

Joined Microsoft in 1980 when Gates talked him into dropping out of Stanford business school. Since replacing Gates as CEO in 2000, Ballmer has been the main decision maker at Microsoft.

He has said he would stay at Microsoft for 9 or 10 years more

Ray Ozzie, 52, Chief Software Architect

Ozzie replaced Gates as Microsoft’s software guru in 2006. His Groove Networks competed with Microsoft before Gates bought the company in 2005. Ozzie is responsible for mapping Microsoft’s software plus services strategy

Kevin Johnson, 47, Pres., Platforms & Services

Johnson has the dual task of protecting Microsoft’s most important business, Windows, and building online advertising. Since joining Microsoft in 1992, he has taken on various roles in marketing including being the head of worldwide sales.

Christopher Liddell, 50, Chief Fin. Officer

Liddell joined Microsoft from International Paper as CFO in 2005 with no background in technology. The New Zealander has played a big role in transforming Microsoft from a company that hoards cash into a more aggressive spender

Brian McAndrews, 49, Sr Vice President

McAndrews joined Microsoft in 2007 as part of the company’s acquisition of digital advertising company aQuantive. McAndrews is expected to spearhead Microsoft’s efforts to create an online advertising platform.

Craig Mundie, 59, Chief of Research & Strategy

Mundie took over as Microsoft’s top technical visionary in 2006 in anticipation of Gates’ exit. His Microsoft career began in 1992 at the consumer platforms division where he developed software for game-consoles and handheld devices.