One in four UK small and medium businesses (SMBs) now use Linux, and more than than half think it robust enough for mission-critical applications, according to a new study.

Two in five of the 200 IT managers quizzed by research firm Vanson Bourne said they had switched to Linux from Microsoft Windows.

Major reasons cited for moving to Linux from proprietary operating systems were lower costs (38 per cent), followed by performance, security and reliability (all at 23 per cent).

"More and more IT departments are willing to deploy Linux," said Nick Davis, EMEA Linux xSeries solutions sales manager at IBM, which sponsored the survey.

"UK customers are traditionally conservative in IT infrastructure but the survey shows they see the benefits beginning to outweigh the costs of changing."

As expected, Unix was the biggest casualty. Sun's Solaris, Hewlett Packard's HP-UX and IBM's AIX were displaced by Linux in 23, 15 and 12 per cent of sites respectively.

IBM's OS/400 lost eight per cent, while Windows NT and 2003 between them lost 42 per cent.

Mike Davis, senior researcher at Butler Group, told vnunet.com: "IT managers are happy to move off Windows NT and it's now crunch time." [Microsoft will shortly end NT support.] But switching from Windows 2003 was a surprise, he added.

So far, Linux has been used most for file and print, web serving and hosting, caching, email and firewall applications. But next year 23 per cent of managers plan to deploy it for business intelligence and data warehousing.

Butler Group's Davis said these applications were the low-cost, high-volume work engine functions requiring solid processing power, where Linux was proven.

Another 15 per cent of the IT managers surveyed are planning to move enterprise resource planning, customer relationship management and other mission-critical applications.

In addition to the 26 per cent of SMBs now using Linux, another 15 per cent said they intend to do so. Only a third had no intention of using it, the survey found. Interviews took place in September.