Every once in a while, an article gets posted somewhere in the blogosphere about how Microsoft needs to release a complete Windows rewrite, something along the lines of what Apple did with Mac OS X. Most people realize that Microsoft is in no position to pull a stunt like that at the moment; it's hard to see Microsoft phasing out support for a billion-Windows-PC-strong user base, but that day may one day come, perhaps thanks to robust virtualization technology.

But in the meantime, Microsoft has settled on rewriting bits and parts of the Windows operating system as it sees fit, with Vista being one of the biggest rewrites (a fact which partially explains the many hardware and software compatibility issues XP's successor experienced at launch). Speculation around a non-Windows operating system in the works at Microsoft has been present for years, but recent trustworthy tidbits of information have found their way into the hands of Microsoft ZDNet bloggers Mary Jo Foley and Ed Bott.

First, let's look at similar projects. MinWin, the slimmed-down Windows core was first shown at a demo last year that briefly discussed how Microsoft was optimizing the aging NT kernel. Singularity, on the other hand, is an experimental microkernel and operating system project started in 2003 for which Microsoft posted the source code back in March. Unfortunately for those interested in a complete rewrite, Singularity was developed exclusively for research purposes and is not intended for practical use.

Codename Midori (I wish Microsoft named it "Doors" instead) is a derivative of Singularity that is meant to supersede Windows, and it is more than just a research project. Still, it is not ready to be previewed and it definitely has not got anything to do with Windows 7. Microsoft has put aside substantial resources and has put many bright people behind the project, which is headed by Eric Rudder, but other than that, very little is known. If it ever does debut, it will probably become available some time before CEO Steve Ballmer retires, nine or so years from now.

According to Foley, one theory is that Midori is another "Cairo" attempt, Microsoft's object-oriented operating system that never saw the light of day. Foley expects Midori to look more like Windows than anything else, and that really isn't much of a surprise: if application compatibility goes out the door, Microsoft needs to at least maintain some sort of user interface familiarity.

Bott, on the other hand, believes that Midori won't be replacing Windows at all, and instead will exist alongside the world's most popular operating system. Bott looks at some Windows history to conclude that Midori will likely debut as something along the lines of Windows NT back in 1993: a complete rewrite that took years to adopt because Microsoft made sure that new versions of both Windows and Windows NT were released.

Bott gives three possibilities for where Midori might be used: special-purpose computers such as those that currently run Windows Media Center or Windows Home Server, virtual server machines, and high-performance workstations. Either way, the Windows platform as we know it today should remain untouched; Windows 7's successor is not going to be Midori.

What's your take: If Midori does indeed arrive one day, what approach makes the most sense for Microsoft?

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