Mary Jo Foley recently blew the lid off Longhorn’s "Dirty Little Secret." Longhorn isn’t going to be based on the .NET Framework, as we all thought. Only a fraction of the total would be written for .NET (Avalon and Indigo), leaving the majority of the operating system as native code.
Unfortunately, I don’t think there was any "lid" on this. When I went to the Professional Developers Conference in October 2003, I didn’t come away thinking that Microsoft was going to rewrite the entire Windows OS in .NET. That would be nuts. .NET, or managed runtime environments in general (including Java), by its very nature demands that something be written in native code. Processors don’t understand .NET IL or Java bytecodes. That means everything, at some point, must be in the language of the processors, which means that most of an operating system will be traditional binaries.