One of the big reasons for the creation of Windows 8's new Start screen is the emergence of tablets. Microsoft has tried and failed on several occasions to create a market for tablet PCs, but the models released during those attempts have always been clunky and difficult to use. The gargantuan success of Apple's iPad--with its streamlined interface and its relentless focus on encouraging content consumption instead of serving as a general-purpose tool--seems to have clarified Microsoft's goals.
Even so, Microsoft is planning to support two types of tablets. The first type, which resembles the company's original Tablet PC concept, consists of convertible laptops running Windows 8. Even Microsoft's Surface Pro is just a thinly disguised laptop that emphasizes touch interaction over keyboard input.
The second type will carry a slightly different flavor of Windows 8, dubbed Windows RT. This version runs only on tablets using ARM processors, rather than Intel or AMD processors. ARM doesn't make its own hardware, but licenses its processor technology to other companies such as Nvidia, Qualcomm, and Texas Instruments. These companies design system-on-chip (SoC) products, which typically consume very little power relative to their performance. (The iPad, for example, uses an ARM-based SoC that Apple designs and builds.)
Windows RT tablets will have a restricted version of Windows 8. Although such tablets will include the traditional desktop, you will have access to the desktop only on a limited basis, to run preinstalled applications such as Office. You will not be able to install desktop programs; instead, RT tablets will focus on the Windows 8 apps you buy through Microsoft's Store.
In contrast, tablets with Intel-compatible processors can run the full PC version of Windows 8, and offer complete access to the desktop. They'll probably cost more than RT tablets, too, as they'll need broader expansion options, bigger batteries, and more memory. Intel-based tablets will almost certainly be heavier and bulkier, as well: For example, Surface Pro, which has an Intel Core i5 CPU, weighs about a half-pound more than Surface RT does.
The existence of two types of tablets on the market may end up confusing consumers, though the differences in price will likely drive shoppers in one direction or the other.
The Microsoft Store