In a twist of irony, the Unix platform celebrates its 40th birthday this year, as does the man whose work probably has done more to diminish the trendiness of Unix than anyone else: Linux founder Linus Torvalds.

Linux and Windows Server outsell Unix by volume. Indeed, given all the attention Windows and the open source Linux platform get, the battle for the mainstream server market can sometimes appear to be a duel between just these two platforms. Unix often seems like yesterday's - or even last decade's - news.

But hold off on any Unix memorial service just yet.

Unix remains a vital cog in enterprise IT and can be expected to remain so for years to come. Figures such as Oracle CEO Larry Ellison attest to its maturity. In a recent public appearance, Ellison endorsed both Linux and the Solaris Unix OS that Oracle wants to acquire as part of its planned $7.4 billion purchase of Sun Microsystems: "We are a supporter of Linux but Solaris is the more mature OS."

A Hewlett-Packard official chimes in that Unix would have a long life similar to how mainframes have continued to thrive. "I haven't seen mainframes [go] away and people were predicting their demise, what, 10, 20 years ago," says Brian Cox, director of software planning and marketing in the HP business-critical systems group. One reason: Unix offers deep integration and higher quality of service, says Satya Scharma, CTO for the company's AIX-based Power systems.

Unix: A stable but consolidating market A sampling of Gartner server shipment numbers does show Unix trailing Linux and Windows Server, as the chart below shows. (If the chart is not visible, you can see it in the original story at InfoWorld.com.)

Gartner chart on Server OS shipments

Unix shipments went from 670,458 units shipped in 2006 to 437,414 units in 2009, with a slight uptick to 451,593 units anticipated in 2012. Linux server shipments for those same years read like this: 1,911,906 units in 2006, 1,682,633 units in 2009, and 1,980,532 units in 2012. Windows Server shipments total 5,416,453 units in 2006, 4,947,891 units in 2009, and 5,699,810 units in 2012. (The marketplace as a whole suffered from the current recession, thus the down numbers for all platforms.) For 2014, Gartner projects Linux shipments of 2,174,334 units, Windows shipments of 6,313,292, and Unix shipments of 474,993.

A user of all three platforms vouches for the maturity of Unix. "It's really at the core of every one of our enterprise systems," says Paul Sikora, vice president of IT transformation at the University of Pittsburgh Medical Center, which runs Unix for its Oracle and cache databases. Unix offers mature redundancy and clustering capabilities, and software vendors are comfortable with their software running on Oracle and Unix, Sikora says.

For example, Unix has been deployed for tougher workloads than Linux and Windows, HP's Cox says: "Unix really has been for what we call the much more demanding kinds of workloads, where you're looking at needing to have data warehouses which go to tens of terabytes." Unix also is the choice for banks, manufacturers, and telecommunications companies running millions of transactions per minute, he adds, because Linux and Windows Server lack the uptime levels needed for such jobs.