Microsoft has 200 programmers working on slimming down the Windows kernel for the next version of the operating system, a company engineer revealed in a presentation last weekend at the University of Illinois.

"A lot of people think of Windows as this really large, bloated operating system, and that may be a fair characterization, I have to admit," said Eric Traut, who holds the title of distinguished engineer at Microsoft. "[So] we created what we call MinWin. It's still bigger than I'd like it to be, but we've taken a shot at really stripping out all of the layers above and making sure that we had a clean architectural layer there."

Traut talked about MinWin last Saturday at a conference on computing sponsored by the university's student-led Association for Computing Machinery. Much of the hourlong presentation was taken up with a discussion of Microsoft's virtualization efforts -- Traut's specialty.

Traut showed off MinWin and bragged about how much leaner the microkernel is than the current core of Windows. While Vista uses 5,000 files for its 4GB core, MinWin weighs in at just 100 files and 25MB.

MinWin is so small that it lacks a graphical subsystem. When Traut booted MinWin, for example, its start-up screen showed the standard Windows flag logo, but the design was built from ASCII characters, a technique discarded decades ago by everyone except spammers.

The microkernel will be used only internally and won't, as Traut put it, be "productized." Instead, it will be the basis of all upcoming versions of Windows, including the next-generation edition now saddled with the code name Windows 7. Microsoft has given out almost no information about that operating system other than a delivery timeline that puts its final release in 2010.

"We'll be using [MinWin] to build all the products based on Windows," said Traut. "It's not just the OS that's running on many laptops in this room, it's also the OS used for media centers, for servers, for small embedded devices."

Microsoft has been knocked in the past for Windows' poor performance and its large size, two criticisms that have been leveled against Vista since its release earlier this year. By stripping the current kernel to the bare minimum -- Traut's MinWin -- and then using that as the code base for Windows 7, Microsoft is trying to reduce the operating system's memory footprint and boost its speed at the same time.

It's probably doing so for good reason, said Michael Cherry, an analyst at Directions on Microsoft, a Kirkland, Wash.-based research company. "This sounds like it's for the new hypervisor Microsoft's been talking about," said Cherry. "It really looks like [in the future] we'll be running some thin hypervisor layer first and then the OS on top of that. So anything Microsoft can do to make that first layer as small as they can is good."

A hypervisor, also called a virtualization manager, is software that allows multiple operating systems to share a single hardware processor. Popular software-based hypervisors include Microsoft's own Virtual PC and VMware's VMware Workstation. Microsoft has been talking up hypervisors and integrating the technology into Windows for years.

"The problem for Microsoft has always been trying to figure out the right balance between putting things in the kernel for performance reasons and pulling them out for stability reasons," said Cherry. "The question here, though, is, can they discipline themselves to not put things into this new microkernel?"

A video of Traut's hour-long talk can be downloaded from or viewed on the conference Web site.