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Gates, a software developer at heart, has driven the company by creating new software for desktops PCs.
Ozzie, with more than 30 years experience developing collaboration software, looks like the man for the job.
His interest in collaboration software began at the University of Illinois in 1973. Ozzie co-developed Plato Notes, a computer conferencing system that allowed staff and teachers at the Education Research Laboratory in the University of Illinois to communicate. He later developed Decnotes, in which he extended the conferencing concept by including a form of instant messaging.
Ozzie worked on developing a PC-based Notes product, and with funding from Lotus founder Mitch Kapor in 1984, established a company called Iris Associates to develop Lotus Notes.
It is this work that has defined Ozzie's career. The experience he gained is now the best hope for Microsoft overtaking its rivals in the online colloboration.
When Lotus Notes first appeared in 1989, the technology to support collaboration was still immature. The product included on-line discussion, e-mail, phone books, and document databases, many of the features that people take for granted today.
IBM bought Notes for £1.8bn in July 1995. In 1997 Ozzie formed Groove networks, which developed software that allowed users to create shared workspaces. Ozzie became Microsoft's chief technical officer when Microsoft acquired Groove in 2005.
"I thought about 'Could we ever hire Ray and his team?' for a long, long time," Gates said at the time of the acquisition.
Ozzie is now responsible for spearheading strategies such as collaborative working and software delivered as a service at Microsoft, in particular Windows Live and Office Live, the company's subscription-based internet services for project and customer management and sales reporting.
"We have discovered that collaboration technology is fairly tough to get right: it lives at the intersection of technology, social dynamics and organisational dynamics," said Ozzie in 2005, when taking up his post at Microsoft. "We hope to apply that knowledge not only to Microsoft Office System productivity technologies but also, given the opportunity, across a range of Microsoft offerings."
As Microsoft's £22.3 billion attempted takeover of Yahoo illustrates, the internet and the delivery of software as a service over the internet is important to the company.
Microsoft and its customers are on a journey towards collaboration over the web. But as the web is a far bigger market than the desktop, where it is far simpler to switch software suppliers, Ozzie will have to make sure Microsoft stands out from the crowd.