Microsoft Adds VHD Format to List of License-Free Technologies

Microsoft has just added its Virtual Hard Disk (VHD) Image Format specification to the list of technologies available for free and without a license under its Open Specification Promise (OSP). Introduced last month, the OSP is Microsoft's "irrevocable promise not to assert" its patent claims on 35 Web services-related specifications. The OSP covers many WS specs (WS-Security, WS-Management, WS-Trust, etc.), as well as SOAP and WSDL specifications.

The VHD file format is designed to capture and store an entire virtual machine (VM) operating system and application stack in a single file. It is used to store information on the state of an app and OS while the program is running, and to start and turn off instances of an app running on a VM.

Microsoft introduced the VHD format in May of last year; it is available now with Virtual Server 2005. According to the company, the file format has been adopted by more than 60 vendors, including Brocade Communications Systems Inc., BMC Software Inc., Diskeeper Corp., Fujitsu Siemens Computers, Network Appliance Inc., Virtual Iron, and XenSource, among others.

The VHD format is a key element in Microsoft's virtualization product stack--and virtualization is a key enabler of Microsoft's long-term Dynamic Systems Initiative (DSI), explains Neil Macehiter, research director at analyst firm Macehiter Ward-Dutton.

"DSI is fundamentally about enabling a more dynamic, responsive IT environment that is more capable of responding to changes in business demand," he says. "Virtualization... is about abstracting away the underlying hardware resource—be it server, storage, or network—so that the physical implementation is unknown: it doesn't matter whether you have one quad server, four uni servers, or whatever. This abstraction is key to enabling the DSI vision."

The announcement that the VHD format would be covered by the OSP was primarily aimed at developers, Macehiter adds. "Virtualization is seen as a key tool in the enterprise IT kit bag," he says, "and Microsoft wants to ensure it's there amongst the other spanners and hammers. [The OSP] provides developers with the assurance that Microsoft will not sue them for use of its intellectual property. There are some constraints and questions remaining about the OSP, but that's really an issue for the lawyers."

Attorney and standards maven Andy Updegrove, publisher of the Web site, greeted the OSP news with some optimism when it was announced in September. In his standards blog, he wrote that Microsoft deserved congratulations for this action: "I hope that the standards affected will only be the first of many that Microsoft, and hopefully other patent owners as well, benefit with similar pledges."

A promise not to assert, which is also known as a non-assertion covenant and a covenant not to sue, is a patent owner's pledge that those who implement the designated IP will not be sued for doing so, within certain limitations, Updegrove explains.

The OSP is similar "in most substantive respects" to the covenant not to assert patents that Microsoft issued last year to cover its Office 2003 XML Reference Schema, Updegrove says. The OSP is more clearly compatible with open source licensing, because the OSP extends to everyone in the distribution chain of a product, from the original vendor through to the end user. Even a partial implementation of a standard is covered.

However, the VHD format is atypical of the specifications included under the OSP, because Microsoft owns the IP for format. The other specs covered by the promise were not exclusively authored by Microsoft (for example, many of the WS-* specs were co-authored with IBM, BEA, and others). This spec, Updegrove points out, is subject to the licensing/IP policies of standards bodies such as OASIS and the W3C, but those policies are not as broad as the OSP in most cases, which leaves a question in the mind of developers regarding the IP of other contributors.

Though some legal questions remain, the OSP is generally good for developers, Macehiter says, and for Microsoft. "IP and patent infringement is a big concern for developers, especially in the open source community," he says. "That concern could prevent VHD from becoming a defacto standard or dominant format. I certainly think that the OSP will reduce the concerns of those developers. And that's really why it's important to Microsoft; it removes the obstacles to VHD being broadly adopted."

About the Author

John K. Waters is a freelance writer based in Silicon Valley. He can be reached at [email protected].