Windows 8.1 is a major update that fixes a lot of complaints users had over Windows 8, and it also brings back the Start button. The new platform comes with all core apps like Mail, Calendar and XBox Music updated, but it also features a new Health + Fitness application.
The Start screen now supports two new Live Tile sizes - a super large one that you can use for example to glance your emails or calendar appointments without having to open the app, and a super small one so you could fit more icons on the screen. Good news is that you can also boot directly into the traditional desktop without seeing the made-for-touch Start screen (that we imagine would be a great option for those who don’t have a touch-enabled devices).
Microsoft also said that devices sold after October 18th will come with Windows 8.1 on board.
source: Windows blog