It'll also bring Media Center as an additional free download.
A Windows 8 upgrade assistant wizard will walk you through the process and point out any incompatibility issues with the machine in question.
Microsoft says the promotion will assist in making the upgrade process as easy as possible and will also extend to buying a physical disc in store, although that option will cost $69.99 (around £45).
Bring your files along for the ride
A post on the Windows 8 blog explains which files and settings users will be able to bring with them, depending on the pervious version of the OS in question.
"It will ask you what you want to keep from your current Windows installation," the post reads.
"You will be able to upgrade from any consumer edition of Windows 7 to Windows 8 Pro and bring everything along which includes your Windows settings, personal files, and apps. If you are upgrading from Windows Vista, you will be able to bring along your Windows settings and personal files, and if you are upgrading from Windows XP you will only be able to bring along your personal files. Of course, if you want to start fresh, you can choose to bring nothing along."
The offer will be open until January 31 and after that new adopters will have to pay full price.
At the time of writing we're not sure whether that mightily reasonable $39.99 upgrade price will convert nicely into £25 in proper money. Stay tuned, Windows 8 fans.
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A technology journalist, writer and videographer of many magazines and websites including T3, Gadget Magazine and TechRadar.com. He specializes in applications for smartphones, tablets and handheld devices, with bylines also at The Guardian, WIRED, Trusted Reviews and Wareable. Chris is also the podcast host for The Liverpool Way. As well as tech and football, Chris is a pop-punk fan and enjoys the art of wrasslin'.