Despite the relentless march of Linux, major vendors believe commercial Unix releases aren't ready for the scrapheap yet.
As Linux evolves from its single-processor roots into larger-scale applications, many market watchers have predicted that it will eventually replace the remaining commercial Unixes: Hewlett-Packard's HP-UX, Sun Microsystem's Solaris, IBM's AIX and SGI's Irix.
"It costs between $150 million and $200 million a year to generate your own Unix system and you then have to say to yourself 'Am I going to see that amount of extra revenue if I put in these features?'" Linux International executive office Jon 'maddog' Hall told iTnews.
However, Unix vendors argue that the needs of large-scale enterprise users haven't yet been met by Linux.
"There'll always be a role for Solaris, and there's tremendous investment in Solaris," said Duncan Bennet, director for infrastructure solutions and software at Sun.
Part of that can be attributed to Sun's increasing focus on making Solaris available for Intel's architectures, as well as its own SPARC processors, he said.
"There's specific things that you might want for specific applications that, for a long period of time, won't be available in Linux," said SGI Australia managing director Bill Trestrail, citing the example of complex real-time applications.
SGI has increasingly concentrated on Linux as a strategic platform. "For the last year, we've been proving extremely large systems in complex environments," Trestrail said. However, the company remains committed to maintaining Irix.
"From our perspective, Linux is going to take a lot of the market share from Unix. Will it take all of it? Probably not.
"There's things that we can do in our kernel as the owner of an operating system to meet the very specific needs of a small community of users that we wouldn't do with Linux, because we're not going to fork the code. We think it will get there but it's not there today."
Other vendors agree that it's hard to predict when Linux will finally supplant Unix.
"It's a crystal ball question," said Geoff Lawrence, Linux business manager for IBM ANZ. "At this stage, there is no prospect of that happening.
"There are a number of commercial Unixes that have atrophied over the years, but if you look at the ones from the key vendors, they seem to be just as strong. They're co-existing quite happily."
HP tells a similar story. "HP has a three OS strategy going forward," said Bdale Garbee, the company's chief technical officer for Linux.
"Our goal is to make sure that Linux is on an equal footing with our Windows and our commercial Unix work in all the ways that matter."
Unix vendors can draw some comfort from recent market data. According to IDC, Unix server revenues were US$4.1 billion in the third quarter of 2003.
While that represented a quarter-on-quarter decline of 3.8 percent, the numbers were up 4.3 percent year on year.
Nonetheless, Linux continues to grow much more quickly, growing 51.4 percent year-on-year to reach US$743 million in the same time frame. As many companies utilise free Linux distributions, revenue data also doesn't fully reveal how many users have taken up the open-source operating system.
"The history of all these Unix systems came from a different time and space," said Linux Internationall's Hall.
"Machines cost $150,000 for a million instruction machine that had a quarter megabyte of memory in it and a 200MB disk, and now you can get a machine for $200 that's a hundred times faster. You can afford to throw away a few cycles of your CPU power because your OS isn't necessarily tailored exactly to your hardware and application."