According to a VMware's announcement Wednesday, VMware ESX 3.5 update 2 has been validated by Microsoft, providing cooperative support from Microsoft and VMware for customers running Windows Server and Microsoft applications including Microsoft Exchange Server, SQL Server and SharePoint Server. VMware ESX 3.5u2 lets one piece of server hardware run multiple operating systems and applications.

"As virtualization emerges as a mainstream technology for customers of all sizes, it's important that they can depend on these technologies to work smoothly with the rest of their infrastructure," said Zane Adam, senior director of integrated virtualization at Microsoft Corp. "Microsoft established the Server Virtual Validation Program to help ensure customers have a consistent and productive support experience when using validated non-Microsoft virtualization software, regardless of the vendor. We are pleased that VMware has joined the Server Virtual Validation Program and along with the other participants can bring the benefits of interoperability to our customers."

Users with support policies for their Windows Server-based applications on VMware ESX 3.5u2 are eligible for cooperative technical support from Microsoft. VMware offers an additional layer of protection outside of Microsoft's Server Virtualization Validation Program, as part of the VMware Premier Support contract with Microsoft, enabling VMware to address application issues rapidly and work directly with Microsoft engineers.

Acknowledging the importance of support for virtualized Microsoft applications, VMware senior product marketing director Bogomil Balkansky said in a statement, "VMware and Microsoft are working cooperatively to help ensure that our joint customers can employ the benefits of virtualization along with the peace of mind that professional product support can provide."

Some commentators like IDG News Service's Elizabeth Montalbano, see this as a strategic partnership as Microsoft encroaches on VMware's 76.4 percent market share reported in 2007, with biggest competitor IBM tailing with 9.8 percent. Microsoft's Hyper-V entered the hypervisor marketplace earlier this year, but appears to realize "it must work with other virtualization vendors, which is why it introduced the validation program last year," Montalbano wrote.