The core code for Microsoft's Windows OS is undergoing a rewrite to make it slimmer for use in a wide range of future products, including Windows 7, the OS that will succeed Vista.

The internal project, code-named "MinWin," is not being readied for a product just yet but will be part of Windows 7, said Eric Traut, a distinguished engineer, during a recent presentation at the University of Illinois. A video of his talk has been posted online.

The kernel is the fundamental code underlying an OS that manages services for applications such as drivers, file management and memory.

"A lot of people think of Windows as this large, bloated operating system, and that's maybe a fair characterization, I have to admit," Traut said. "But at its core, the kernel, and the components that make up the very core of the operating system, is actually pretty streamlined."

Traut showed a demonstration of MinWin, which lacks a graphical user interface. It takes up just 25MB when stored on disk, compared to the massive 4GB the full Windows Vista OS needs, Traut said.

MinWin can run on less than 40MB of RAM, he said. "That's kind of proof there is actually a pretty nice little core inside of Windows," Traut said.

But Microsoft still wants to shrink it. "It's still bigger than I'd like it to be," Traut said.

Microsoft uses its kernel in a range of products, from its client Windows OS to servers. Keeping the kernel as small as possible enables it to be used in OSes for lower-memory environments, such as embedded devices.

"This will provide us the ability to move into even more areas," Traut said.

Microsoft has said it will release Windows 7 by 2010, although the company has not revealed much detail on its features.