Windows 8.1 pre-order opened

Months after the release of the windows 8.1 preview (Windows Blue) , the official version will finally arrive in a few weeks.

This big update will be available to current windows 8 users for free in the Windows Store on 17/10. While users who are using an older Windows OS will need to pay 119.99 US for Windows 8.1 or 199.99 US for Windows 8.1 Pro. Both versions will come with a copy of Windows 8.1 for them to use for installing virtual machines, backup and clean install.

Note that Windows 8.1 does not support Windows version before Windows 7, so if you are using Windows Vista, Windows XP or older versions and you want to upgrade your computer to Windows 8.1, you need to purchase a copy of Windows 8 and then update it through Windows Store by yourself.
Pre-order it now

Source:
Microsoft