Last year, Microsoft announced Surface Laptop, which ran a new version of its Windows 10 operating system called Windows 10 S. This year's Surface Laptop 2 doesn't have it, but some other new PCs do - but what is it? 

The key thing is that when using Windows 10 in S Mode, you probably won't know that there's any difference to Windows 10 Pro, apart from the different stock wallpaper. It looks the same and works the same in most instances. 

What is Windows 10 S or Windows 10 in S Mode?

Windows 10 in S Mode is described as a fully-functional version of Windows that's designed to run smoothly on all hardware. Microsoft hasn't revealed exactly what the S stands for, but says that it's evolved from features that teachers have asked for. 

Those things include things like faster log-in, better battery life and easy management across large numbers of devices. Microsoft has demonstrated that a new user logging on to a Windows 10 S will be able to get into the PC faster than a standard Windows 10 Pro PC. 

You can only run verified apps from the Windows Store

The big catch with Windows 10 S is that it's designed to only run verified apps from the Windows Store. You will not be able to download apps online and install them; this version is effectively sandboxed.

That's a big disadvantage for many users but Windows 10 in S Mode is meant for education or environments where you don't want users installing their own apps.

That means it's potentially more secure, but it also means that Microsoft knows exactly what software it's going to be dealing with and should mean that power demands can be matched, without some scrappy rogue app sitting in the background eating power and hogging resources.

If a person using Windows 10 S tries to install an app from outside of the Windows Store, it will be stopped, but you'll then be offered an alternative that's from the Windows Store, so verified by Microsoft.

There aren't any hardware restrictions on Windows 10 S either, as it's designed to run across a full range of devices. Microsoft is working on compatibility with a wide range of third-party accessories and devices because you'll have to have drivers signed by Microsoft to be able to use them with Windows 10 S.  

What devices will run Windows 10 in S Mode

Intel-based PCs intended for education use may be supplied in S Mode. One entire group of devices for which S Mode is enabled is if they are based on ARM processors. Currently, this means ultraportable PCs that run Qualcomm's Snapdragon processor such as the HP Envy X2. That's because ARM processors aren't compatible with programs written for Intel or AMD processors. They will run universal apps from the Windows Store though. 

Can you upgrade Windows 10 S to Windows 10 Pro?

Yes, you can. You can upgrade a Windows 10 S device to Windows 10 Pro with just a few clicks and an update. That will remove the restriction on app installs so you can use it just like any other Windows 10 Pro PC.