Longhorn, Centro, Cougar, and the ever-humble "Home." What's with all the names? Well, now that Vista is well on its way -- sales reputed to be 40 million and climbing -- Microsoft appears to be shifting its attention to a dizzying array of variations on its Windows Server operating system.

The sweet spot of Microsoft's Windows Server OS strategy, which was explained at WinHEC, is pretty much your standard product road map. There's the full-sized version, Windows Server 2008 (download a free Beta 3, here), which is the operating system formerly code-named Longhorn.

Then there are a couple of down-market spins, in the form of Centro, a midmarket product, and Cougar, aimed at small businesses. Both will ship in 2008.

Far more interesting, though, is the "Home" product, which amounts to an entirely different beast. Unlike its Longhorn-related cousins, Windows Home Server is built on the older code base of Windows Server 2003.

More interesting, it's not really intended to be a server operating system the way one typically thinks of server operating systems. (That's because, over the years, server operating systems have become more enterprise or simply "bigger than desktop" operating systems, rather than "server" operating systems, per se.)

As best as I can tell, Microsoft seems like it's pitching Windows Home Server less as an operating system for a home computing system and more as as an excuse to get you to install a big honkin' storage setup in your home.

Check this out: it's a preliminary data sheet [PDF] for HP's MediaSmart Server. The machine is basically a 1.8-GHz AMD Sempron PC in a tower with a whole lotta hard drive bays (four, in fact).

Microsoft's Windows Server Home home page (try saying that three times fast) points up this storage angle with its marketing pitch:

"With Windows Home Server, you can store your music, photos, and other files on a central hub-like hard drive, accessible from every PC in your house. Protect your files and your PCs with automatic backup and a simple restore process -- even gain access to files on your PCs from anywhere with an Internet connection through secure Web access."

Ah, I get it! It's the world's biggest iPod.

Still, Microsoft may be on to something here. We're getting to the point where many people have so many PCs scattered throughout the house that a consolidated storage solution -- a server that actually serves -- isn't such a bad item.

Interestingly, this line of thinking also spotlights the fact that we've reached the point where equipping yourself for heavy-duty home computing now often costs you more for memory and storage than for the main processing engine that powers the thing. That's the case for the HP MediaSmart Server, whose Semprom processor goes for a paltry $30.

P.S. Here's a PC Mag review of the Windows Home Server Beta 2. And here's where you can download Microsoft's Home Server SDK.