It’s official, Microsoft is not offering Windows Phone 8 to existing handsets. We exclusively revealed Microsoft’s plans back in April, and the reaction generated Windows Phone discussions far and wide. Speaking to The Verge ahead of the Windows Phone 8 sneak peek today, Microsoft’s Greg Sullivan revealed the reasons behind the company’s choice not to offer a direct upgrade from Windows Phone 7.x to Windows Phone 8.

Describing some of the latest hardware changes in Windows Phone 8, that we outline here, Sullivan explained that "the nature of the investment [in Windows Phone 8] is primarily in areas that are not exploitable by existing hardware." Windows Phone 8 introduces support for multi-core processors, amongst other things, so the "Lumia 900 getting support for using dual-core or NFC doesn't mean a lot," says Sullivan, "because it doesn't have the hardware to take advantage of that." Microsoft decided to focus its efforts on Windows Phone 8 to make it as good as it possibly could. "To do the work to bring all of those elements to a platform that can't exploit them wasn't necessarily the most efficient use of resource," explains Sullivan.

Some existing devices get Windows Phone 8's new Start Screen UI

Instead, Microsoft plans to bring a new Start Screen interface to existing devices through a Windows Phone 7.8 software update. "It's basically bringing the core elements of the Windows Phone 8 start experience, and UX, right to existing phones," says Sullivan. Microsoft isn’t detailing all of its Windows Phone 8 UI changes today, but the new Start Screen will include support for tiles across the entire screen and a new smaller tile layout — you can read more about the changes here.

"When you pull that Lumia out of your pocket after you've received that 7.8 update, it will look and feel the same as a Windows Phone 8 device," claims Sullivan. "Because you don't have a multicore chip and don't have some of these other elements, it didn't make sense for us to make those investments for devices that couldn't really exploit them." We pressed Sullivan for details on which devices will be upgradeable to Windows Phone 7.8, but he wouldn’t reveal specifics. "I think it's safe to assume to latest generation of devices are a primary target," he said, pointing to the Lumia 900 as an example of a device that the company wants to "keep fresh."