Standards wars, such as the Blu-ray vs. HD-DVD battle, can keep many potential users on the sidelines until a winner is declared. Virtualization software vendors are trying to avoid just such a battle over the adoption of virtual appliances.

Such appliances are software bundles containing an operating system and application that have been pre-configured and tuned to run in a virtualized environment. The idea is to ease and speed up deployment of new virtualized applications, but that's contingent on the virtual appliances being able to work with various virtualization technologies, such as VMware's ESX Server, Citrix Systems' XenServer and Microsoft's new Hyper-V software.

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Those three vendors, along with IBM, HP, and Dell, have been working since last year with Distributed Management Task Force Inc., a Portland, Ore.-based standards group, to create an interoperability specification for virtual machines. And they're now far enough along on the specification, called the Open Virtual Machine Format -- or OVF, for short -- to build tools that conform to it.

Citrix, which bought its way into the server virtualization market by acquiring XenSource last year, announced Tuesday that it plans to offer tools for creating virtual appliances that can run on multiple virtualization hypervisors, whether they're from Citrix itself or VMware, Microsoft, and other vendors.

The new tools, which are being developed under an initiative called Project Kensho, are aimed at users as well as ISVs and are scheduled for release in a technical preview during the current quarter.

Simon Crosby, CTO for Citrix's virtualization and management division, said the OVF specification is critical to the adoption of virtual appliances. If the virtualization market were to bifurcate around different formats, "it really ruins a lot of the benefits of virtualization," Crosby said. He added that in addition to the obvious benefits for ISVs, enterprises could use OVF to make their internally developed applications platform-independent.

Chris Wolf , an analyst at Burton Group in Midvale, Utah, said that OVF Version 1.0 is primarily a specification for distributing virtual machines and importing them into customer environments, and that he thinks the specification has some ways to go before it becomes really useful. For instance, the spec needs more development to enable users to manage the appliances in a heterogeneous environment, Wolf said. But he added that he thinks the vendors and the DMTF are on the path to accomplish that in later releases of OVF.

As the dominant vendor in the virtualization market, VMware has the most to lose by backing an interoperability specification. But Wolf sees VMware's support for OVF as being linked to its desire to get the investment it has made in management tools to pay off.

Virtual appliances are still limited in use, and Wolf said that Microsoft, for one, is heading down a different path with its support for streaming applications to the desktop.