Windows and Linux operating systems are getting an ever-growing share of datacentres, according to Gartner.

This is because inexpensive x86 servers are taking over jobs once the domain of Unix operating systems, but that said, Unix use still remains core in datacentres.

While Unix’s revenue share is predicted to stay flat for the next five years - from $16.4 billion this year to $16 billion in 2012 - Gartner analysts say that users of major Unix systems from Sun Microsystems, IBM and Hewlett-Packard have nothing to worry about.

"Nobody is achieving great growth, but nobody is dying," said Gartner analyst John Enck, of the major Unix systems, adding that "there is stability."

Gartner, at its datacentre conference this week, said Windows is expected to get $19.6 billion this year rising to $22.2 billion by 2012. Linux, meanwhile, will grow from $8.6 billion to $12.2 billion over that same period.

"As a market, we want less complexity, we want fewer operating systems," said Enck.

Users will also continue to seek to simplify their environment, often by cutting back on the number of operating systems where possible. In an audience poll, the majority of attendees - 80 percent - were either reducing the number of supported operating systems or maintaining that number, with just one-fifth opting to add to their operating system mix.

Reducing the number of supported operating systems in a datacentre is easier said than done, said Frank Muller, senior director of IT technology and infrastructure support at HealthPartners, a health care provider, who was at the conference.

Muller said he supports AIX, Windows, Linux, a mainframe system and HPUX. When he asked the provider of one application that runs on HPUX to move it to AIX, the vendor complied. So far so good.

But a year and half later, Muller said he ended up moving the application back to HPUX because he couldn't get the vendor's long-term support for keeping the application on AIX. "If the vendor isn't there from an application-point of view, I don't think you will make much headway," he said.

The total operating system in the server market is just over $54 billion this year, with $9.5 billion in the category of "other" encompassing all the other operating systems such as OpenVMS, mainframe operating systems and other Unix systems.