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Microsoft’s ‘Viridian’ Gets Open Spec Promise

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To encourage developers to write tools that work with its coming virtualization hypervisor, Microsoft has announced that it is making the applications programming interfaces (API) for its upcoming Windows Server virtualization hypervisor a part of its Open Specifications Promise, or OSP, initiative.

The company quietly released the news via a post on its Windows Virtualization Team Blog.

Analysts said the company is so far behind the competition that it couldn’t afford not to make the technology open.

A hypervisor is a small, specialized operating system that sits on the server hardware and lets the server run more than one operating system above it. Microsoft already offers two virtualization products – Virtual PC and Virtual Server. But both require Windows to be running at the bottommost layer.

Other vendors, primarily VMware, have already offered hypervisor-based virtualization for several years. Microsoft has said that it will release its own hypervisor technology that ultimately will be part of Windows Server 2008. However, that technology will not initially come with Windows Server 2008 when it ships in the first quarter of next year.

Instead, Windows Server virtualization, or WSV, is due out within 180 days of the shipment of Windows Server 2008. It’s also referred to by its codename, Viridian.

While Microsoft is bound to be a player in the server virtualization arena due to its massive dominance in the server market – when it does ship its hypervisor, the company will still lag behind VMware. Additionally, in August, Citrix Systems bought out open source hypervisor vendor, XenSource, which is popular on Linux servers.

Given that interoperability among hypervisors is something customers need, adding the APIs under the OSP license is good news for everyone, according to Citrix, which is now both a Microsoft partner and competitor.

“This will allow us to ensure that virtual machines created on XenServer will be compatible with Microsoft WSV when it is delivered as a component of Windows Server 2008,” said a statement attributed to Simon Crosby, CTO of the Virtualization & Management Division at Citrix, as part of the Windows Virtualization Team Blog posting.

Much of Microsoft’s pitch regarding virtualization has been to developers – particularly those working on systems management tools to enable administration of virtual machines (VM) and the hypervisor that controls them.

Microsoft’s OSP basically promises that developers can use protocols, APIs and other technologies that are placed under that aegis, freely and without fear of lawsuits – as long as they don’t sue Microsoft.

The so-called “hypercall APIs” – which enable third-party developers to write applications and tools that work with WSV — will be available when Windows Server 2008 is released to manufacturing, probably later this year. However, developers and other partners have had access to the specifications since 2006.

Given its late entry, several analysts say, Microsoft has to do everything it can to be thought of as a team player. IT shops have heterogeneous environments already and that’s not going to change any time soon. So everything has to work together, one way or another.

“Microsoft is really behind other [competitors] in the virtualization sphere, so in many ways they don’t really have any choice, because a lot of [IT] organizations are already using virtualization from other companies,” Michael Cherry, lead analyst for operating systems at researcher Directions on Microsoft, told “Those organizations are going to want a high-level of interoperability among devices,” he added.

Cherry pointed out that a year ago Microsoft also put its Virtual Hard Disk (VHD) formats under the OSP licensing initiative.

Other analysts agree its crucial for Microsoft to gain developers’ trust in this area.

“In Microsoft’s case, where a lot of people are deeply suspicious of the company’s motives, they needed to do this,” Gordon Haff, principal IT advisor with analyst firm Illuminata, told “Given that they don’t have their own virtualization software out there yet, this is the kind of thing they need to do to remain part of the conversation.”

Indeed, some observers take it as conventional wisdom that Microsoft’s sheer dominance over the Intel server market means WSV is destined to become the standard. Microsoft argues that should be the case since they are the largest operating system vendor.

However, this may turn out to be a case where Microsoft’s dominance doesn’t prevail.

“Being it’s Microsoft, Windows Server’s strong market position is going to be seeding the market [for WSV] but VMware is the gorilla in this particular market,” Dwight Davis, vice president at researcher Ovum Summit, told “I don’t think [WSV] is a slam dunk as the dominant hypervisor,” he said.

This article was first published on

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