With the Windows Phone Summit coming to a close last week, we got to see what Windows Phone 8 has in store for us, come this fall. Unfortunately, the WP8 update will not be rolled out to existing WP7 and WP7.5 handsets - the initial official statement puts the blame squarely on the hardware requirements for WP8. However, Mashable's chat with Microsoft’s senior marketing manager for Windows Phone, Greg Sullivan, has revealed more details.
GSMArena - The new core that enables so many cool features (multiple CPU cores, better graphics) is shared with Windows 8 RT (based on Windows NT) and not Windows Phone 7 (based on Windows CE, same as Windows Mobile).
Microsoft’s senior marketing manager for Windows Phone, Greg Sullivan, says that it's not impossible to port WP8 on older devices, but the cost of doing that would be very high and the benefit very little - WP8 enables multi-core support, higher resolution screens, NFC, microSD card support and so on, none of which will make a difference on the legacy hardware.
Instead, a WP7.8 update will facilitate partial WP8 features on existing WP7 and WP7.5 handsets, the most important of which is the new Smart Screen. Meanwhile, Windows Phone 7.5 apps will certainly run on WP8 devices; however, there's no backwards compatibility for WP8 apps due to the fact that these apps will require better hardware. Check out the video of an early build of Windows Phone 7.8 running on the Lumia 900 below: