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Windows 8.1: Installation and new features

The new update for Windows 8 is available since October 17, 2013. How to install Windows 8.1 and what are the new features available?
The "Start" button is back under Windows 8.1.

Left click to open the startscreen.
Right click to access to features such as Control Panel, Task Manager and devices and shutdown options.

While appearance is similar, 8.1 brings more customization options:

4 sizes of thumbnails
Use the same wallpaper for the desktop and startscreen.

Windows 8.1 provides the ability to perform searches (on your computer and on the web) from your desktop.

The cloud service is fully integrated to Windows 8.1.

Among the new options :

Manage passwords.
Configure SkyDrive..
Configure the Search module.

Migration from Windows XP and Vista to version 8.1 is not recommended by Microsoft. Technically, it is possible to update a PC when its configuration meets the minimum requirement.
In this case, you will have a fresh installation of Windows (8.1). It is strongly recommended to backup all your data and applications.

Follow the procedure described here http://windows.microsoft.com/en-us/windows-8/upgrade-from-windows-7-tutorial

Migration of Windows 8 to Windows 8.1 is the easiest to achieve.
The creation of an installation DVD or USB key is not required , unlike other versions of Windows.
FAQ from Microsoft