As Red Hat prepares to launch the Red Hat Enterprise Linux 5 operating system on Wednesday, the question is again being asked whether a robust and feature-laden operating system (OS) is really needed for some computing situations.

Makers of "software appliances" are using the launch as an opportunity to predict that the days of the monolithic OS are numbered. They say the future lies in a modular system in which software runs with only enough lines of OS code to make it work.

Some see promise in the appliance alternative to the OS, while sceptics think large enterprises will still need a general-purpose OS.

The same questions arose recently around the launch of Microsoft Windows Vista. A trio of Gartner analysts published a report in 2006 that said the increasing complexity of Windows makes it "unsustainable." Gartner predicted Windows will be broken up into modular components.

The same could be said for Red Hat Enterprise Linux 5 (RHEL 5), said Billy Marshall, CEO and cofounder of rPath, a software appliance platform vendor.

As new features are added to it, RHEL 5 has become just as unwieldy as Windows, Marshall said. "It's bigger and more bloated."

OS vendors add all sorts of functionality in the event some enterprise may want it, and the addition of these features is one of the reasons why both Microsoft and Red Hat have encountered delays bringing their products to market, he said.

Installing an OS could use as much as 1.82G bytes of space on a hard drive, he said. A software appliance with only the code to run one application would use just 300M bytes, he said.

"The general-purpose OS model is breaking," Marshall said.

Another software appliance vendor, Ingres, on 27 February launched a database management software appliance it calls "Icebreaker" to compete against IBM's DB2 and Oracle's database software.

Software appliances may have a place in some niche environments in which a customer needs to run just a few pieces of software, said Jay Lyman, an analyst with The 451 Group. But a larger business would probably still need the various programs that are bundled into an OS, he said.

It might be possible to run an enterprise infrastructure without an OS, Lyman said. "But then again, you've already got people [in your IT department] running the OS, and it's a pretty critical part of the infrastructure."

Rather than seeing OSs fading, "I think we're seeing the trends going the other way," said Adam Jollans, director of worldwide strategy for Linux and open source at IBM.

At a time when IT administrators want to get more out of their existing hardware, isolating software applications and running them only with small pieces of code seems counterproductive, Jollans said.

"Many more people want to run multiple applications and do many different things...so I think we need the generic operating system to support all the different things people want to do," he said.