According to analyst firm Gartner, Vista will be the last version of Windows that exists in its current, monolithic form.
Instead, the research firm predicts, Microsoft will be forced to migrate Windows to a modular architecture tied together through hardware-supported virtualisation. "The current, integrated architecture of Microsoft Windows is unsustainable - for enterprises and for Microsoft," wrote Gartner analysts Brian Gammage, Michael Silver and David Mitchell Smith.
The problem is that the operating system's increasing complexity is making it ever more difficult for enterprises to implement migrations, and impossible for Microsoft to release regular updates. This, in turn, stands in the way of Microsoft's efforts to push companies to subscription licencing.
The answer, according to Gartner, is virtualisation, which is built into newer chips from Intel and AMD, and has become mainstream for x86 servers through the efforts of VMware. "Once Windows includes virtualisation at its core, we expect OS development to change direction from integration to modularisation," the analysts wrote.
Virtualisation is best known as a way of running multiple server instances on a single hardware platform, but it can also be used to run individual operating system functions or applications. The technique isolates the various components from one another, making them easier to manage. Gartner believes Microsoft will use virtualisation to divide the Windows client into a "service partition", controlling system functions such as management and security, and one or more application partitions. Such a path is already being followed in the x86 server world, Gartner said.
"The combination of the service partition and the ability to deliver horizontal functions in software appliances provides the key for unbundling the Windows OS," the analysts wrote. Such an architecture would allow Microsoft to make major development changes to Windows without worrying about disrupting dependencies across the entire operating system. This, in turn, would mean the company could release regular updates, and would make backward compatibility easier.
Next-generation Windows-based partitions "could run in parallel to partitions running kernels with the Vista/NT code base," wrote Gammage, Silver and Smith. They said Microsoft doesn't agree with this vision, saying it's identified problems with integrating data across partitions and creating a consistent user experience. "However, we regard these concerns as only partially founded, and anticipate a key role for virtualisation in the required unbundling of the Windows OS," the analysts said.
Gartner expects a significant update to Vista in late 2008 or 2009 that will add virtualisation (in the form of a component called a hypervisor) and a service partition. The hypervisor will allow more frequent updates, and will make the Software Assurance subscription scheme effectively mandatory for Windows from around 2010, Gartner said. To date, Microsoft's main effort to simplify Windows development, in 2004, was to rebuild Windows into a stack of more than 50 layers, Gartner said.
"Upper layers could have dependencies on lower layers, but lower layers could not be dependent on upper ones," the analysts wrote. "This would allow it to lockdown lower layers when complete and worry less about compatibility changes as it worked up the stack." But this redesign is not enough to ease Microsoft's ongoing development and delivery problems, or the deployment difficulties of enterprises, Gartner said.