Microsoft is buying virtual-machine technology from Connectix Corp., an established maker of VM products for Windows and other operating systems, as a way of making it easier for customers to migrate and consolidate Windows NT apps on the upcoming Windows Server 2003.

Terms of the deal were not disclosed.

The deal, disclosed Wednesday by Microsoft, addresses a key concern among businesses evaluating Windows Server 2003. In a recent survey of 719 business-technology professionals by InformationWeek Research, 63% indicated that application compatibility is a concern with Windows Server 2003.

Virtual-machine technology helps address compatibility issues by serving as a middleware layer between an older application--say, a custom app developed in Visual Basic for Windows NT 4--and a new operating system running on the latest Intel-based hardware. In addition to supporting application migration, VMs make it possible to consolidate multiple apps on a single server. "One of the things we're very focused on is building an attractive path to a modern operating system for our NT 4.0 installed base," says Jim Hebert, general manager in Microsoft's Windows Server product-management group.

Microsoft will acquire three products, along with related core engineering and support teams, from Connectix, a private company. They include a VM for running Windows apps on Apple computers, one for running multiple older Windows apps on a single Windows desktop PC, and a VM for Windows servers. Connectix revealed the latter product, which it calls Virtual Server, in September. There will be no interruption in availability of the desktop VMs; the server VM will be available from Microsoft by year's end, after extensive testing, Hebert says. Connectix execs weren't available for comment.

That presents a timing problem for any Windows NT 4 customers who might be anxious to upgrade to Window Server 2003. That's because Windows Server 2003 is scheduled for release in April, while the VM for Windows Server 2003 may not be ready until eight months later. "It certainly could be less than eight months, and we have a lot of interest in making it less," Hebert says. Next year could be an even bigger year for Windows NT migration because Microsoft has indicated that it will stop certain kinds of support for Windows NT at the end of 2004.

Virtual machines are just one way to move applications from Windows NT to Windows Server 2003. Others include recompiling apps or, on some servers, partitioning them to run on one part of the computer. VMware Inc., a Connectix competitor, earlier this week announced the ability to run a single virtual machine across multiple CPUs.