One of the first things Windows 8 chief Steven Sinofsky said in the Build keynote this week was that all the demos were "equally at home on ARM and on x86." However, besides that statement and our brief look at the Developer Preview running on an Nvidia quad-core Kal-El reference tablet, Microsoft remained relatively tight-lipped on the new architecture support — especially on when it will release the ARM version of Win 8 to developers and how it plans to address the fact that future ARM PCs won’t run x86 desktop apps. Sure, there were a few ARM tablets hidden behind glass with a static Start screen, but it's really been from chatting with Microsoft and executives from Nvidia, Qualcomm, and TI that we’ve started to put together the pieces of what Windows 8 on the low-power architecture is going to look like, at least in respect to form factors and apps. It’s going to be much bigger than just that tile-based interface on a tablet — hit the break to see what we were able to dig up.

Form factors

"Assuming ARM equals slate is wrong," Microsoft’s VP of Windows Planning Mike Anguilo told us. And that was certainly the message we heard throughout the show from Nvidia, Qualcomm, and others. Nvidia’s Rene Haas told us that the interest in other form factors, including laptops and "ultrabook-like" clamshells, is "overwhelming," as is the interest from OEMs in building Windows 8 Kal El systems. (Nvidia’s CEO hinted at the same thing just last week.) Haas also told us that "Kal-El is much more comparable to a Core [Intel Core processor] than an Atom in terms of raw computer power." So we'll take that as a "watch out netbooks!"

Similarly, Qualcomm’s Steve Horton said "there’s no restriction on form factor in Windows 8," and that "nothing restricts us from being in tablets, all-in-ones, and laptops." When we asked him if he thought Windows 8 could finally make the smartbook (remember those laptops with smartphone guts that never took off?) a viable category, he seemed to nod his head. "Clearly we see Windows 8 as representing an opportunity to look at that space again."

Legacy apps

But putting Windows 8 on ARM-powered laptops and desktops makes the legacy situation even more pressing. How am I supposed to explain to my mom that a new ARM-powered laptop, which has the Metro UI and the traditional desktop, doesn’t run older Windows applications? (Note: we've seen multiple times this week that the regular desktop view is part of the ARM build and that the Store will have a mix of apps — both Metro and regular x86 desktop apps.) Obviously, it's not news that older x86 apps won't run on ARM-based tablets — Microsoft clearly stated that back at CES, and again yesterday — but how Microsoft plans to explain that to end users is still a bit hazy. And the truth is that it seems that there’s going to be more to the story in the coming months.

When asked about Microsoft’s plans to explain the legacy program situation, Angiulo said that "there is a significant amount of marketing that we are capable of doing that can get through — we can afford to tell a story and tell it long enough and clearly enough. We will make sure it is absolutely clear where your legacy apps will run." However, he followed that up with a kicker: "porting things and whether we open native desktop development are either decisions that are either not made or not announced yet." Similarly, Qualcomm's Horton stated that "there’s more to come in terms of the legacy issue as it relates to ARM." Whether those two quotes taken together means Microsoft will announce some sort of porting strategy remains unclear, but it certainly implies that Microsoft's not done explaining the whole story.

Speaking of the entire legacy app story not being complete, remember the version of Office that Microsoft recompiled for ARM and showed at CES? When we asked Angiulo about Office he said, "we didn’t make the promise of shipping it or announce a SKU, but I showed it running, so you do the math." He even went on to say, "so, you have potentially an Office solution that’s real Office and you have all these Metro style apps, you almost start thinking, at what point is it [the lack of legacy apps for ARM] not confusing anymore."

We're not sure that extinguishes all the confusion, but while Microsoft hasn't committed to anything when it comes to legacy apps on ARM, from what we can tell there's a bigger porting story to come. And the fact that the company clearly intends to ship a real version of Office for ARM is a big step in understanding that ARM Win 8 devices aren't meant to be an entirely different class of computer. Bottom line: While we've gotten a promising sketch of what Windows 8 on ARM will look like, it's clear Microsoft has a lot more coloring to do.