If you hit up the MSDN Subscriber Downloads page, and then click Details under the version that you’ve obtained from elsewhere, you’ll find the SHA-1 hash. While we’re not going to write a guide on how to obtain Windows 8.1 RTM from non-official sources, we will at least tell you to check the SHA-1 hash of the ISO that you download to make sure that it’s legitimate. If you don’t want to wait for October 17 or 18, there are two options for downloading Windows 8.1: You can obtain a copy (and a license key) from a friend/colleague with an MSDN, TechNet, or DreamSpark (student) subscription, or you can download a Windows 8.1 RTM ISO from your favorite file-sharing website (The Pirate Bay, Mega, etc.) To download and install Windows 8.1 for free, follow the guide below. If you’re using another operating system (Windows 7, Windows XP, OS X), you can either buy a boxed version ($120 for normal, $200 for Windows 8.1 Pro), or opt for one of the free methods listed below.
If you’re using Windows 8, upgrading to Windows 8.1 is both easy and free.
