Microsoft previously has made such pledges only in the Web services arena, where it faces tougher open standards competition. Now the company's Open Specification Promise allows "every individual and organization in the world to make use of Virtual Hard Disk Image Format forever," Microsoft said in a statement. VHD is a way of packaging an application with that application's Windows operating system. Several such combinations, each in its own virtual machine, can run on a single piece of hardware.
Microsoft is following the example of VMware, the market leader in Intel and AMD x86 instruction set virtualization. VMware made its Virtual Machine Disk, or VMDK, specification available in April.
Despite its game of open one-upmanship with VMware, Microsoft retains a lever of control over VHD. Open Specification Promise prevents Microsoft from withdrawing the present standard from users, but the company retains the right to revise or rewrite VHD.
VMware, owned by EMC, is also a strongly proprietary company. Although it has published the details of VMDK, it, too, has kept the right to change it.
"If either of these companies were different, they might open the format 100%," says Gordon Haff, an analyst with market researcher Illuminata. But going the 100% route would mean submitting a proprietary specification to a standards body. There's very little difference between the two vendor specs, Haff says, and a standards body could collapse them into a single virtualization standard.
Neither company is likely to let that happen. Instead, the growing number of businesses embracing virtualization will get used to dealing with two virtual file formats for a long time to come. "Going all the way doesn't come naturally to either [company]," Haff says.
On A Roll
Regardless of whether one is more open than the other, VMware is building up a head of steam that even Microsoft can't ignore.
Last quarter, VMware projected sales of $630 million over the next 12 months if it maintained its revenue growth rate. In the latest quarter, it raised its run rate projection to $750 million.
In one of the fastest-growing software markets, Microsoft soon will face a $1 billion-plus competitor, but Microsoft is still trying to get its hypervisor virtual machine out of the starting blocks. Hypervisors are the future of virtualization because they run more efficiently than previous virtualization technology and make use of advances in Intel and AMD processors that speed up virtual machines. Microsoft's hypervisor is due sometime after the launch of Windows Longhorn Server, now projected for the second half of 2007. VMware is already marketing its ESX Server hypervisor.
Making its VHD spec open leaves Microsoft at less of a disadvantage in the virtual market. Users of VMware's ESX Server can import Microsoft's VHD files and will be less wary about doing so. Likewise, open source Xen virtualization software can import VHD files.
But Microsoft's bid for more openness still falls short when it comes to one fast-growing area of virtualization: virtual appliances.
Virtualization users want their applications arriving prepackaged in a virtual file format with an operating system. That can happen under VHD or VMDK, but Microsoft charges for each virtualized copy of Windows. Dan Chu, VMware's VP of emerging products and markets, says of Microsoft's Open Specification Promise, "You can be very public about making something open, then restrict it on the other hand."