The newly launched Red Hat Enterprise Linux 5 operating system features a modular design that counters the argument by critics that operating systems are becoming too large and complex, a Red Hat executive said at launch ceremonies in San Francisco.

Red Hat Enterprise Linux 5 (RHEL5), Red Hat's first new open source operating system in two years, was also formally unveiled at events in London, Singapore and Hanover, Germany.

Critics say this is the beginning of the end of the OS. CEO of software vendor rPath, Billy Marshall, touts the software appliance alternative. Rather than buy a large operating system with features not needed, an rPath customer can buy a software platform that pairs the application with just enough OS code to make it run. Marshall described RHEL 5 as "bloated", similar to his assessment of the new Windows Vista OS from Microsoft.

But executive vice-president of engineering for Red Hat, Paul Cormier, said RHEL 5 lets customers loaded only the OS features they chose.

"We have built in a very modular fashion. You can load or install whatever you want," Cormier said. "If you don't want to install the domain name system [DNS] components you don't have to. We have been able to pull in storage components and management components if you so choose."

With RHEL 5, Red Hat eliminates the AS and ES designations for different levels of OS. Instead, there is Red Hat Enterprise Linux and Red Hat Enterprise Linux Advanced Platform. Customers who already use Red Hat Enterprise Linux ES can upgrade to RHEL 5 at no change in their subscription price. Likewise, current users of Red Hat Enterprise Linux AS can upgrade to RHEL 5 Advanced Platform at no change in subscription pricing.

RHEL 5 includes a virtualisation feature that allow the OS to run up to four guest environments, meaning that one copy of the OS could be run virtually on four other servers. RHEL 5 Advanced Platform allows the user to run an unlimited number of virtual versions of the OS. Red Hat offered both server and storage virtualisation, Cormier said.

RHEL 5 is available now and is being loaded on servers as requested at companies such as HP and Sun Microsystems. Sun supports multiple OSes, even if they compete against Sun's own Solaris 10 operating system.

"[Red Hat has] put some pretty good things in the OS, but a lot of them are things that we've had in Solaris for a very long time," group manager in Solaris Software at Sun, Larry Wake, said.

Red Hat also will launch a new partner program later this year called Red Hat Exchange that brings together key open source application software vendors whose products could be sold through the vendors or Red Hat.

"It brings open source providers together in one place with a standard subscription agreement and one throat to choke for support," vice-president of corporate development for Red Hat, Michael Evans, said.

Among the open source vendors already signed up to join the Exchange are MySQL, a database provider; SugarCRM, which specialises in customer relationship management; and Zimbra for email and other messaging systems.