This IDC study provides a top-down sizing of the operating systems and subsystems market (measured by revenue) in 2004 and a 2005?2009 forecast for this market. During 2004, the operating systems and subsystems market grew at a surprising 8.7%, above IDC's previous expectations. This growth was led by Windows in terms of net new dollars, with Windows revenue growing by 10% and increasing its total from $12.5 billion to $13.8 billion. Microsoft now captures 67% of the revenue in the market. By comparison, Linux, which grew revenue by an impressive 38.6%, captured under 1% of the market total. The Western Europe and rest of the world (ROW) regions produced the greatest growth contributions.

"The growth of the operating systems and subsystems market was surprisingly healthy during 2004," said Al Gillen, research director of System Software at IDC. "This revenue growth was led by Windows, but what made the overall market growth possible was the unexpectedly strong growth posted by the Unix and mainframe platforms."