The popularity of pre-packaged Linux servers continues to roll on.The market for server hardware shipping with Linux reached more than $900 million in the second quarter of this year, according to research firm IDC. Revenue grew by almost 50% from the same quarter a year ago, and numbers of units shipped were up 38%.Growth was not quite as dramatic as it was in the first quarter of 2004, when Linux server revenue grew by 57% and units grew by 46%.Still, nearly reaching the $1 billion mark in sales isn\u2019t bad. IDC says Linux accounted for about 8.4% of overall server revenue. The research firm expects Linux server revenue and shipments to continue to be strong over the next few years, as adoption of the 2.6 Linux kernel drives more enterprises to deploy Linux in more mission-critical server applications.As for the competition, Windows as a server operating system increased its revenue by 13.2%, while the number of Windows server shipments jumped by 25%, IDC says. People seemed to be buying more Unix servers, with shipments up 20.2% from the same a year ago, but the business was not a moneymaker for vendors, as Unix revenue dropped 3%.IDC estimates that by 2008, 29% of all servers shipped will have Linux running on them (Linux accounted for 12% of shipments in 2003). The firm also sees Linux pulling in around $9.7 billion in revenue in five years, accounting for 15% of the projected $60.8 billion server market worldwide.