Windows 8.1 Preview and Windows RT 8.1 Preview are pre-release versions of Windows 8.1. The updates include enhancements in personalization, search, apps, the Windows Store, and cloud connectivity, and have security and reliability features.

Users currently may upgrade to Windows 8.1 Preview from Windows 8 and Windows RT (RT 8.1). Windows 7, Windows Vista and Windows XP users will be offered the final version of Windows 8.1, which will be a free update for Windows 8 later this year through the Windows Store.

Let's see what's new for Windows 8 Preview:

• First of all, Windows 8.1 adds two new tile Let's see what's nnew for Windows 8 Preview. First of First of all, Windows 8.1 adds two new tile sizes: large and small. Now you have a total of four options for displaying programs and other objects.
• The start button is back. A simple click takes you to the Start screen. The right-click power user's menu has also a new set of Shutdown options:
  

• In Windows 8, changing a tile's properties is complicated. The Windows 8.1 update lets you select a group of tiles and resize, move, pin/unpin, or uninstall them with one click.
  
• The modern/Metro Windows 8 Control Panel has been incomplete, forcing you to revisit the desktop to accomplish many simple customization tasks. In Windows 8.1 PC Settings is much richer, with new options available.
  
• Windows 8.1 is also bringing on board one of the most popular programs missing from the operating system - a Faecbook app. In addition, Flipboard, which lets users combine articles into a digital magazine, and the National Football League will also create apps for Windows 8, coming at Windows 8.1.
• The Apps screen is a swipe away or available with the click of an arrow on devices that don't have a touchscreen. You can arrange apps in any of the four orders shown here, making it easier to find apps without searching.
• Apps and files get synced across all your Windows 8.1 PCs and tablets. If you change your Start screen, install new apps, pin new apps to the Start screen on one PC - that all will get synced to your other PCs.
  
• The Windows Store has been also redesigned, making it easier to find apps. And several of the apps that come with Windows 8 have been updated for Windows 8.1.
• If you want to configure a Windows 8.1 PC to work as much like Windows 7 as possible, you can bypass the Start screen at startup, show the Apps view automatically when you go to Start, and list desktop apps first so you're not distracted by unwanted Windows 8 apps.
  
• Windows 8.1 also features a single search, which now brings you results from your PC, your apps, and the web.
• Windows 8.1 will also update apps automatically, and the Bing search engine will recommend new ones for you based on what you've used before.
• Windows 8.1 also supports 3-D printing. Microsoft said that making a 3D object on your PC will be as easy as writing a document in Word and sending it to print. Windows 8.1 adds plug-n-play support for printers, enabling apps to submit 3D print jobs, understanding 3D file formats, and connecting lots of apps with lots of hardware to deliver an end-to-end solution for customers. Staples announced that it will start selling 3D Systems? Cube 3D printer for $1,299 at the end of June, and several companies are offering consumer-friendly 3D printers that range from $800 to $3,000.
• There's also a hands-free mode, which can be useful while cooking. Instead of touching the device with messy hands, Microsoft says, you simply wave your hand over the camera to flip through a recipe.
• Bing has cooked up a pair of new apps - Bing Food & Drink and Bing Health & Fitness - and they're both included in the preview.
  Bing Food & Drink app features a library of recipes from popular food websites, cookbooks and bloggers, along with cooking tips from some of the world's best chefs. Bing Health & Fitness puts nutrition, fitness and medical information in one package. You can track your diet, exercise and health history in the app, and sync it with Microsoft's HealthVault to pull in your medical records and information from devices such as blood glucose monitors, electronic scales and FitBit.
• The photo app is now more robust, with tools for cropping, retouching, and editing photos. Windows 8.1 also has the ability to do a video chat over Skype from the lock screen. You can also see a slideshow of your photos from that screen.
• Internet Connection sharing is also back in Windows 8.1. You can set up a PC or tablet so that other devices can share its broadband connection instead of chewing through precious mobile data.
• SkyDrive is now the default location for saving documents. So you always have your files wherever you go, even when you're offline. And with the included SkyDrive app, you can manage both local files and SkyDrive files in one place.
  
• Microsoft also unveiled new capabilities with its Bing search technology, including better maps. The Windows 8.1 maps app will come with 3-D imagery, which developers can embed in their own apps.
• When you get Windows 8.1 Preview, you also get to check out the new Internet Explorer. Internet Explorer 11 Preview is built for touch, with faster load times, a full-screen experience that includes side-by-side browsing of your sites, and real-time info delivered on your Start screen through live tiles for your favorite sites.

Microsoft strongly recommends that only experienced PC users download Windows 8.1 Preview or Windows RT 8.1 Preview, since they are still under development. In addition, in order to use Windows 8.1 Preview you must sign in to your PC with a Microsoft account. The option to create a local account will be made available at the final release of Windows 8.1.

Besides downloading the updates through the Windows Store, you may also install them by downloading an ISO, butt this option would require you to use the following product key: NTTX3-RV7VB-T7X7F-WQYYY-9Y92F.

Microsoft will also make available a preview of Windows RT 8.1. However, have in mind that you won't be able to restore Windows RT after you install Windows RT 8.1 Preview, so you'll have to wait for the final version on the OS.

In addition, uninstalling any of the new WIndows updates isn't supported, unless you restore your entire system to its factory condition.

Windows 8.1 Preview is available in Arabic, English (US), Chinese (Simplified), Chinese (Traditional), French, German, Japanese, Korean, Portuguese (Brazil), Russian, Spanish, Swedish, and Turkish.

Seperately, Microsoft executives also demonstrated Project Spark, a simulator unveiled at the E3 video game conference in Los Angeles this month. It invites gamers to craft virtual worlds with the swipe of a finger, and then play through them on the Xbox One.

Kinect for Windows developer community

Microsoft also today at Microsoft BUILD 2013 made two announcements for Kinect for Windows developer community.

First, starting today, developers can apply for a place in our upcoming developer kit program. This program will give participants exclusive early access to everything they need to start building applications for the new generation Kinect for Windows sensor, including a pre-release version of the new sensor hardware and software development kit (SDK) in November, and a replacement unit of the final sensor hardware and firmware when it is publicly available next year. The cost for the program will be US$399 (or local equivalent). Applications must be received by July 31 and successful applicants will be notified and charged in August.

Additionally, in September Microsoft will again refresh the Kinect for Windows SDK with several exciting updates including:

• The ability to extract the user from the background in real time
• The ability to develop Kinect for Windows desktop applications by using HTML5/JavaScript
• Enhancements to Kinect Fusion, including capture of color data and improvements to tracking robustness and accuracy