Existing Windows users are in for a real treat! During Windows 10's release preview's unveiling on the 21st of this month, Microsoft revealed that existing Windows 7, 8.1 and Phone 8.1 users will receive a free upgrade till one year of Windows 10's is release. Yeah, after an year you'll have to shell out money to upgrade or buy a new Windows 10 license. The move is seen as Windows' drive to retain existing customers and attract new ones in the process. And Microsoft has never allowed a this big upgrade for free in the past. A free upgrade for Windows Phone users is also a welcoming move as Apple has allowed for free upgrades for OS X since Mavericks and also for iOS. Even Android upgrades are free. This probably works very well with with existing users who buy the device just once and upgrade whenever a new OS is ready. This lack of free upgrade in Windows meant more users sticking to old versions even when later ones have been released. Not to mention the cost of buying a new Windows license. Users looking for a free copy of Windows simply pirated it. Now Microsoft has got all these covered. But on the flip side, Windows 7 is still the most popular desktop operating system in the world right now with a lions share of 56.26%, according to web analytics firm NetMarketShare. Windows 10 has a lot ground to cover if it wants to pip Windows 7 for pole position. The new features like Cortona, Spartan and a redesigned UI are expected to do the trick for Microsoft.