And Windows 7 has been aggressively adopted by users.
Microsoft most recent sales figure for Windows 7 was 450 million licenses as of September 2011, up from 240 million in October 2010. Just as tellingly, Web metrics company Net Applications said Windows 7 powered 38% of all Windows PCs in November, an increase from 22% 12 months earlier.
Gillen was more optimistic about Windows 8 on tablets, but warned that Microsoft had to coax that market to be successful.
Gillen said that the key to Windows 8's success on tablets lay in Microsoft's ability to convince developers that the operating system deserved their attention. If the company can persuade developers to rework existing Windows applications for 8's Metro interface and craft new mobile-centric apps, it has a chance.
"[But] if it is unable to marshal the developer community to invest the way needed -- and over the past several waves of Windows releases the company has not succeeded at this task -- the future is bleak," Gillen said.
While Gillen gave Windows 8 little hope for scoring the kind of upgrade success enjoyed by its predecessor, he was adamant that that didn't mean Microsoft itself was irrelevant.
"You can't declare Microsoft irrelevant when their OS ships on more than 90% of new systems," Gillen said.
Microsoft declined comment on IDC's Windows 8 prediction.
Sign up for Computerworld eNewsletters.