Sun Microsystems has become the latest server manufacturer to offer Windows Server operating systems pre-installed on x64 servers, as well as what Sun's EVP John Fowler described this afternoon, during a press conference call, as "the entirety of our server product line."

Solaris will be able to work in a Microsoft virtualized environment, and Windows will be able to work under a virtual machine hosted by Solaris, under a collaboration agreement announced today. Fowler said 100% of Solaris' customers also run Windows someplace in their data centers, so this agreement was vitally necessary.

Today's agreement represents an expansion of a landmark pact between the two companies in 2004. At that time, they decided to coalesce on a number of projects, the culmination of which has not always garnered public attention (more on that in a moment).

For now, the expansion covers three areas of joint business: 1) Sun signing on as an OEM reseller of pre-installed Windows for x64 servers; 2) Microsoft and Sun enabling each other's operating systems to run in their own virtualized hosts; and 3) the two companies setting up a new interoperability test lab for certain joint projects.

Sun decided that as long as an indisputable majority of its Solaris customers run Windows, and an undetermined but presumed majority of its x64 server customers run Windows, Sun may as well pre-install Windows Server 2003 on those servers.

"Obviously with Solaris, we have an operating system that already has built-in virtualization," Fowler told reporters today, "and that's available at no cost. So we can do applications as well as OS virtualization with Solaris. But Solaris doesn't necessarily solve all customer problems, and so what we are doing obviously here is collaborating with Microsoft. They [have a] very serious effort around virtualization and their new Viridian platform, and we're very excited to connect up our engineering leadership with theirs in a collaboration to see how to make these environments work together.

Sun will be enabled to offer support to its own server customers using Microsoft software, including SQL Server and Microsoft Exchange. "This isn't necessarily about a competitive landscape," Fowler added. "It's about the fact that 100% of Sun's customers run both Windows and Solaris. So it's a very natural thing for us to work together on these technologies."

However, at two points in today's press conference, Fowler was asked to say how many Sun customers run Windows, though he responded that would be very difficult to estimate, explaining that x64 servers are sold both directly through Sun and through channel partners. "We know that the percentage of Windows has been growing pretty rapidly, in particular with high-scale platforms like the X4600...but the exact percentage is very, very difficult to actually get to.

"We have been steadily growing our portfolio and our market presence in the x64 space," he added. "We have seven quarters of growth now, and we're on the cusp of introducing our next generation Galaxy platforms. So from a maturation standpoint, we're at a good point of expanding our offerings."

At the same time, Fowler indicated that Sun is keeping tabs on this agreement, stating quite clearly at two points that the OEM resale provisions are limited to Windows Server 2003 and not yet the 2008 edition.

Still, the virtualization portion of today's provisions will enable Sun to collaborate with Microsoft on Viridian, the project for supplying virtualization support for Windows Server to system hardware. Windows Server Virtualization had been scheduled to become a part of WS2K8, though last May Microsoft decided to delay its release until a later revision, perhaps in a service pack.

Answering a question about scheduling that had not been asked, Microsoft corporate vice president for server and tools marketing Andrew Rees told reporters today, "Viridian is on the same schedule that it's been on before. This is about providing additional support for Solaris running on it. It won't change in any way, shape, or form. Our current plans are on track for Viridian."

Lees also stated the two companies' interoperability lab has already officially launched, though with a minimum staff. Its numbers are expected to rise quickly, with project deadline goals having been set for the next 60 to 90 days, specifically for projects dealing with interoperability.

With Microsoft also having announced an interoperability lab with Novell, asked Network World's John Fontana, why didn't the three companies just simply build one big lab rather than two little ones? "There are different locations," responded Lees. "Some of the subject matter may be common - like, for example, the Novell lab in Cambridge is part of something on a completely separate track, although some of the technologies may end up being common, like virtualization - a fairly cross-cutting piece of technology."

But Fontana pressed on: Isn't the point of interoperability to interoperate? "We will make sure that virtualization technology works across different platforms," Lees spelled out. "We've already been doing that in support for Linux, for a variety of different versions of Windows, and now Solaris. There's some level of overlap, and we'll make sure that the technology works."

BetaNews asked, would customers start to see some of the benefits of this expanded agreement through more support in Microsoft administrative tools, such as its System Center line, for managing heterogeneous networks that also include Solaris-based servers? Microsoft's Lees responded by saying we should already be seeing those kinds of tools, on account of the companies' 2004 collaborative agreement.

For instance, he went on, Sun and Microsoft already worked together on WS-* Web services management interoperability, and he himself played a role there. "In fact, I did a demo two years ago in front of 10,000 IT professionals, which showed a Sun machine running Solaris and System Center Operations Manager - we did some things to the hardware, it recognized that, and it corrected the fault.

"We've been talking about this to customers," Lees added with a chuckle, "but it doesn't make good press coverage that the companies are working well together, instead of less controversially. That's a column-inches problem in the press."

At one point, Sun's Fowler said he found it challenging to make announcements over the past three-and-one-half years of its collaboration with Microsoft concerning the products of their labor. "Some of these announcements did not necessarily generate an enormous amount of press because they were not controversial," he said.

He mentioned the two companies worked together for WS-Federation in Sun's directory management products for interoperability with Active Directory, Exchange, and SharePoint; and Microsoft's storage APIs were already integrated into Sun's storage products to enable integration with Windows.

Fowler declined to predict how many x64s with Windows Server his company will sell before the end of the year, though he stated the company has already created new product SKUs and is taking pre-orders from select customers now.