Shop around online and it won’t be long before you come across cheap versions of Windows 10 on sale. These might be very tempting, especially if you're looking to upgrade from Windows 7 now that its support has ended. Some of the inexpensive versions will no doubt be of a dubious nature, while others seem legitimate. So, what are they and should you buy one for your PC? We break it down.

What is an OEM licence?

Many of the cheap versions you'll see on eBay and other links will be something called an OEM version. OEM stands for Original Equipment Manufacturer and is a term applied to companies that build PCs. Those desktops and laptops usually include a copy of Windows, so that when you walk out of Currys/PC World with that shiny new Dell you can take it home and use it immediately.

While the majority of OEM versions end up preinstalled on PCs, it’s also possible to buy them as licence keys from places like eBay or Lizengo. This is a common practice for users who like to build their own gaming PCs, or buy a second-hand device that has either no OS, or one that is out of date.

How is an OEM licence different to a retail version of Windows?

Most people never buy a copy of Windows itself. They buy a PC that has Windows on it, and that’s the last they think of it.

But those who do want to purchase the operating system often opt to pick up a retail version. These are either sold in standard software packaging in shops, and thus called boxed copies, or are available online from Microsoft as a download and licence key.

Microsoft's price for a download version of Windows 10 is £119.99/$139 for the Home edition or £219.99/$199 for Pro. Compare that to eBuyer's £103.49, or the even cheaper options online over on Amazon. Lizengo's price for a Windows 10 Home OEM key is just £22.99, or £32.99 for the Pro Edition.

 Whats difference between Windows 10 OEM and retail versions

In use, there is no difference at all between OEM or retail versions. Both are full versions of the operating system, and as such include all the features, updates, and functionality that you would expect from Windows. 

Where their paths diverge is in two important areas: support and flexibility.

When you buy an OEM copy you’re in essence taking on the role of the manufacturer of your device. This means that if you run into problems with hardware compatibility or encounter activation issues, calling Microsoft for help will probably end up with you being told to contact the manufacturer of your device. Which of course, in this case, is you!  

The second major difference is that whereas when you buy a retail copy of Windows you can use it on more than one machine, although not at the same time, an OEM version is locked to the hardware on which it was first activated.

This might not seem a major issue, but if you decide to change the motherboard on your PC, then chances are you’ll also need to pay out for a new copy of Windows at the same time, as the old one won’t re-activate on the new hardware.

To see how you can reuse your retail Windows licence read our How to install Windows on more than one PC feature.

Should I buy a cheap OEM key?

There’s nothing illegal about buying an OEM key, so long as it’s an official one. There are plenty of legitimate sites online that deal in this kind of software, Amazon has a number of sellers offering OEM keys, as does eBay, and more specialist sites like the aforementioned Lizengo are an option.

Just be sure to read the description carefully and check user ratings before spending any money. Some very cheap offers might be for foreign copies of Windows 10, which may require downloading an English language pack, but these are free and available from Microsoft.  

So long as you’re happy to take on the responsibility of being your own technical support, then an OEM version can save a lot of money while offering an identical experience.

Of course, those who prefer peace of mind, and someone at the end of the telephone who can help fix any problems, might prefer the full retail route instead. Just avoid buying a USB flash-drive version from that dodgy-looking guy in the Tesco car park.