The Linux operating system will account for 29% of units shipped into the worldwide server market in 2008, up from 12% last year, according to IDC.
Linux will take $9.7bn (£5.3bn) from the $60.8bn market when measured by revenue, it predicted.
Servers running the Windows operating system will account for $22.7bn of the market.
IDC forecasts that the worldwide market for server hardware will grow at 3.8% per year for the next five years, jumping from $53bn in 2004 to $60.8bn in 2008.
Growth will be strongest in central and eastern Europe and the Asia Pacific region, both of which are expected to grow more than 6.5%, year-over-year, until 2008.
Though Windows systems will account for 37% of the 2008 server market, when measured by spend, they will account for 60% of the units shipped, a slight drop in market share from the 63% of units shipped that IDC reported for 2003.
Sales of blade systems are also expected to grow rapidly, according to IDC. By 2008, blade shipments are expected to reach $9bn, or 29% of server units shipped. Blades accounted for just 4% of the server market in 2003, the research firm said.
Robert McMillan writes for IDG News Service