Microsoft has not announced anything yet about its SKU -- officially, "stock-keeping unit" (unofficially, meaning version) -- plans for Windows 10, other than the fact that there will be more than one when the operating system launches this fall.

But that hasn't stopped the flow of questions, guesses and tips about which Windows 10 variants will work on which types of hardware.

Before wading into these murky waters, a quick note on terminology. Publicly, Microsoft is going to brand all variants of Windows 10 as plain-old "Windows 10," company officials confirmed last week during Microsoft's Windows 10 event on January 21. But there are actually a number of different Windows 10 flavors that Microsoft has developed and/or is developing that are tuned to run on different hardware.

The version of Windows 10 that is available in test form right now is Windows 10 Desktop. This flavor runs on Intel-based PCs, laptops and hybrid/2-in-1 devices. The version of Windows 10 that will be available in test form starting in February 2015 is Windows 10 mobile. That version is optimized to run on ARM-based Windows Phones (from Microsoft and other OEMs), as well as on ARM- and/or Intel-based small tablets, ideally under eight inches in size.

There is a custom version of Windows 10 inside the Surface Hub -- the conferencing system that Microsoft announced last week. There's a different custom version of Windows 10 that will power the HoloLens augmented-reality goggles Microsoft showed off last week. And there are a slew of different Windows 10 embedded variants in the works, including Windows 10 Industry and a Windows 10 Internet of Things (IoT) SKU, which Microsoft officials didn't detail at all last week (codenamed "Athens"), that will work on Intel- or ARM-based devices.

Here's where things get a bit more complicated.

There are two things that the Softies are referring to as "desktop" with Windows 10. There's the aforementioned Desktop SKU (which I am capitalizing to distinguish it); and then there's the desktop mode. With Windows 8, the desktop was a separate environment where users could run Win32 apps. In Windows 10, Microsoft is allowing users running the Desktop SKU to run their Win32 applications in windows, rather than requiring them to use a separate desktop to do so.

With Windows 10, Microsoft's SKU plan is more about what OEMs want and customers expect, as opposed to dictates as to what is or isn't the right chipset or feature set, from what I'm hearing from my contacts.

The Windows 10 mobile SKU is aimed at devices where running Win32 apps doesn't make sense, so it won't support a desktop mode. It will be customized to run "Modern"/Universal apps from the unified Windows Store. The Mobile SKU is aimed at devices with small RAM and disk requirements. It's built for locked down devices, though, in theory at least, it could run on a device with any size screen.

The Windows 10 Desktop SKU will be the more general purpose SKU. It will run on anything with an Intel chip, just like Windows XP, Windows 7 and Windows 8. The Windows 10 Desktop, technically, will be able to run on devices of almost any screen size (including existing 7-inch Intel-based tablets, as Microsoft's Joe Belfiore tweeted yesterday). The question is will most users want to look at Win32 apps on screens that small? If they do -- and if OEMs think there is a market for small Windows 10 devices that can run legacy apps -- new, small-screen size Windows 10 devices running Windows 10 Desktop will come to market.

So, the Windows 10 Desktop SKU can run Modern/Universal and Win32 apps in either tablet (full-screen) or desktop (windowed apps) modes. The Windows 10 mobile SKU can only run Modern/Universal apps and only has full-screen app mode.

Because Intel (finally) began delivering chipsets that are competitive with ARM in the medium/larger tablet space, PC makers began using those chips, enabling them to run both Win32 and Modern and Universal apps on a single device, starting late last year. ARM is still important for phones and small tablets, but with Intel stepping up its game, Windows 10 Desktop devices running Win32 and Universal apps look to be more competitive with Chromebooks right now than do ARM-based Windows 10 devices that can't run Win32 apps.

Here are a few Windows 10-related tidbits we don't know (but may know relatively soon):

Will Microsoft build/field any more ARM-based Surface tablets? I've consistently heard from sources that this is not in Microsoft's plans. But no one from Microsoft has said this publicly. Given Intel chip advances and the preference by many business users to be able to run both Win32 and Modern/Universal apps, my bet is no.

Will users of the existing ARM-based Surfaces (Surface RT and Surface 2) get enough Windows 10 features to run the coming version of touch-first Office for Windows 10? We know (because Microsoft execs said so last week) that ARM-based Windows 8 devices will get an "update" with a subset of Windows 10 features some time in the coming months. But we don't know which features or when, so we don't know about next-generation Office compatibility.

Can Windows Phone and small tablet users running Windows 10 mobile SKUs connect monitors, docks, mice and keyboards to their devices and use them that way? I know Windows Phone is/was missing support for the Bluetooth Human Interface Device (HID) keyboard protocol, but haven't heard anything more (so far) about use in these scenarios.

We also don't yet know how many Windows 10 editions Microsoft will make available to customers. I'd assume there will be at least Windows 10 Home, Pro, Enterprise and Mobile versions, but Microsoft is unlikely to get specific about this -- or about the pricing for these until closer to the fall launch of Windows 10.

For now, we know Microsoft plans to make an upgrade SKU for Windows 7, 8.1 and Windows Phone 8.1 users available for free for a year from the time it launches Windows 10. But we don't know how much Windows 10 will cost consumers after that one-year promotion, nor how much Microsoft plans to charge business users for Windows 10 (who aren't already paying for upgrade rights as part of their volume licensing plans)....