IBM is extending its support for Sun Microsystems' Solaris operating system to cover more of its x86 servers and blades, the two vendors announced Thursday.

Under the agreement, IBM will distribute Solaris OS and Solaris Subscriptions for some of its System x servers and BladeCenter blade servers. The servers include BladeCenter HS21 and LS41 servers as well as IBM System x3650, System x3755 and System x3850 servers.

IBM already supported Sun's flavor of Unix on some of its BladeCenter servers, but it wasn't a formal relationship.

The move is part of IBM's strategy to offer users a range of operating systems and Sun's desire to have Solaris run on a wider set of hardware. IBM has its own AIX flavor of Unix and also supports Microsoft's Windows operating system and Red Hat's and Novell's SUSE distributions of the open-source Linux operating system.

Jonathan Schwartz, president and CEO of Sun, described the new partnership as a "tectonic shift" in the marketplace.

IBM and Sun have long been strong and aggressive competitors in terms of both the server and Unix operating systems markets. Both Schwartz and Bill Zeitler, senior vice president of IBM's systems and technology group, were keen to emphasize that the tie-up shouldn't be seen as either party giving up on its respective products.

"I don't see a single operating system as being the choice," Zeitler said. "Customers and markets make choices. Mature vendors react by responding to those requirements." While IBM continues to invest in AIX and sees it as an "excellent, highly scalable and reliable offering," the vendor is also a pragmatist, he added. "A lot of customers love Solaris and are loyal to it."

Under the terms of the formal agreement between the two companies, IBM becomes a distributor and reseller of Solaris, the only leading hardware vendor, other than Sun, to have that capability. While IBM will distribute Solaris, Sun will provide support for the operating system.

"I can tell you our deal with HP is arms-length," Schwartz said of an existing relationship with Hewlett-Packard around Solaris running on HP's ProLiant servers. "They're not an OEM. Our relationship with IBM is really the strongest with any partner in the marketplace and will hopefully set the tone for other relationships. IBM stands alone," he added. Schwartz wouldn't be drawn on whether Sun is in talks with Dell about having Dell servers support Solaris.

"I'm very proud to be the first of the Tier 1 vendors who will have an agreement with Sun like this," Zeitler said. "I imagine we're not the last, but I'm pleased we're the first."