Microsoft officials have continued to hold to the party line that the Windows Phone 8 software development kit (SDK) would be out "this summer." But on July 26, a preview of the SDK leaked to the Web, exposing some of the announced -- and still officially unannounced -- next-generation Windows Phone features. As Windows SuperSite's Paul Thurrott noted, the emulator in the SDK allows developers access to the new Start screen for the phone, which will include three tile sizes that can be altered by users via touch. (This same Start screen is what Microsoft and its carrier partners will be delivering at some point to existing Windows Phone users in the form of the Windows Phone OS 7.8 update. Microsoft officials are not providing a timeframe as to when 7.8 will be out. I've asked.) The new emulator also exposes the still unofficially announced data-usage metering feature (originally known as Data Smart and now, apparently, called Data Sense); the announced Microsoft Wallet; new Zune-less music and video branding; and mentions of the three supported screen resolutions. (The Data Sense image in this post is courtesy of the Windows SuperSite.) Most interesting -- to this architecture-diagram-obsessed reporter, at least -- is this programming-interface comparison chart, which LiveSide.Net discovered in the documents around the SDK. This chart shows which of the application programming interfaces (APIs) are shared by the Windows Phone 8 OS, Windows 8 and Windows RT. There is some overlap, but there are also a number of APIs that are unique to the phone platform (indicated in white in the diagram). Microsoft officials said last month that while Windows Phone 8 OS and Windows 8/Windows RT would share a "common core," the two platforms did not use or expose the identical set of APIs. In other words, it is not technically correct to say that Windows Phone 8 OS is "based on" the Windows RT framework, as I've seen a few sites claim. Microsoft is on a path to unify to the greatest extent possible the development tools and frameworks used by its Windows, Windows Phone and Xbox content developers.
(A related aside: Microsoft Research helped with some of the work involved in replacing the Windows Embedded Compact core in current Windows Phones and Windows Mobile phones with the Windows NT-based core. That effort was known as "Experiment 19.")