IBM is to distribute Sun Microsystems' Solaris operating system on its x86-based rack and blade servers.

Big Blue is the first tier-one vendor partner for Solaris, making it the strongest partnership for bundling operating systems with hardware to date, Sun chief executive Jonathan Schwartz said in a conference call to unveil the agreement.

The bundling agreement also spans collaboration on optimising drivers and the operating system itself to run on IBM hardware. IBM is also considering supporting Solaris on its System Z mainframes.

The partnership raises questions about the competition between the two vendors, both of which are now able to offer virtually identical systems.

However, Bill Zeitler, vice president of the Systems and Technology Group at IBM, argued that IT vendors are no longer required to differentiate through offering closed hardware and software stacks, but by offering a broad selection of choices.

"We are not trying to force the client into one operating system or the other," Zeitler said. "If Solaris has characteristics that you like, we would like you to consider our hardware platform."

Charles King, a principal analyst at Pund-IT, typified the trend as "essential pragmatism".

"A large number of companies happily use and prefer Sun's Solaris as their business operating system. IBM's decision to become Sun's first tier-one original equipment manufacturer reflects that reality," King wrote in an analysis.

HP currently supports Solaris on some of its server hardware, but the relationship between HP and Sun is "at an arm's length", said Schwartz.

Dell also has publicly stated that it is considering supporting Solaris.