Windows RT is a relatively new OS - it's only been around for an year now and it is different from both the regular Windows and the Windows Phone OS you may have seen elsewhere. RT (short for Runtime) is made to run on ARM processors (like the ones in today's smartphones and tablets) instead on the regular Intel and AMD processors that we use in our computers.
Windows RT relies only on the Windows Store for apps and you can't install any legacy software. None of your Windows Vista/7/8 apps are directly available on Windows RT, unless their developers release a compatible version and Microsoft claims that making one is pretty easy.
Another important difference is that Windows RT is only available pre-installed on devices and it's not available directly to end users - only OEMs have access to it. After the initial enthusiasm, the OEMs in question have started moving away from the platform.
Right before the Lumia 2520 was announced, there were even rumors that Microsoft will be scrapping the project altogether. So far (November 2013), there is no official announcement on the matter.
The exact version which the Nokia Lumia 2520 boots is Windows 8.1 RT. The latest version of the ARM-based OS is not a major update, though it still brings some welcome changes to the table.
You can see the Lumia 2520 with Windows 8.1 RT in action below.
The Start menu is comprised of live tiles just like on Windows Phone. The difference is that the live tile grid is scrollable horizontally rather than vertically, which makes sense given the default orientation of the screen.
A pinch gesture on the screen shrinks the grid of tiles, which is particularly handy if you've got a lot of tiles and you are starting to get lost.
A swipe from the top or bottom of the main screen reveals the context menu. This gesture is enabled in every app, as well as on the Start screen. When in the latter, it reveals the "Customize" menu.
To select a tile you need to do a vertical swipe on it - mass selection for unpinning and uninstalling is also available. This works on all sorts of files in Start - pictures, documents, etc.
Live tiles can be resized just like in Windows Phone - there are four sizes available now as opposed to three in Windows 8 RT. An option to turn live tiles off is also available. Some tiles are nothing more than static icons even after you make them bigger but others (like Calendar) help bring more information right on your homescreen.
Swiping up from the Start menu reveals the full list of installed apps. A pinch gesture reveals an alphabetical grid which lets you quickly search the list of apps.
Switching between apps is done by swiping from the left edge of the screen towards the center. There's an alternate way of doing this - a short swipe from the left edge of the screen and then quickly back displays a vertical thumbnail grid of the recent apps. If you're using a conventional keyboard with your Windows 8.1 RT, a simple Alt+Tab gets the job done just like it has for ages now.
Split screen mode has been greatly revamped in Windows 8.1 RT. It now allows users to view apps side by side in equally-sized windows, as opposed to a large and a small one in the previous version.
The Charms menu is available across the OS. It's accessible via a swipe from the right edge of the screen and gives access to search, share, Start, devices and settings.
Devices detects every device in your network's Home/Workgroup - if you're logged on to one that is. You can send content to these devices through this menu. Share does the same, but using different apps to share depending on the type of content.
The settings menu gives you quick options for Wireless, sound, screen, notifications, power and keyboard.
There are sliders to adjust the brightness and volume of the device.
You can also select which keyboard to use and choose to restart, shut down or sleep using the quick toggles.
There's also a shortcut to the detailed settings menu here. From there you can personalize the look of Windows 8.1 RT. You can choose lockscreen wallpaper, select apps that can run in the background and show notifications or detailed statuses on the lockscreen - for instance the Calendar will display your upcoming events.
The next option is the Start screen. You can choose a color scheme and background. There are many options in every color you can think of but you can't use your own picture as wallpaper - you have to select one of the preinstalled ones.
There's an option to change your account photo as well. It is done by tapping on the top right corner where the user account information is located.
You can add multiple users on Windows 8.1 RT, just like you can in Windows 8. Users can have their own tile grid, apps, preferences, etc. If you have more than one Windows 8 or RT device you can enable settings sync between them.
Notifications can be disabled on the lockscreen altogether and you can switch off the sounds. You can also configure which apps can push notifications to your lockscreen. However you cannot control the way notifications are presented, only switch them on and off.
Users can choose which apps to use while searching. There's the handy option to delete the search history too. Sharing settings are very limited. Currently you can only share via Mail, People and SkyDrive.
The general settings handle time, spelling, screen automatic brightness, language options, reinstall Windows, etc. The Devices section handles the PCs and devices in a Wi-Fi Home/Workgroup. You can add new and connect with existing ones.
Windows 8.1 RT lets you choose which settings you wish to sync with SkyDrive or disable the feature. Your personalization, passwords, app, browser settings and more can be synced between your PCs.
Modern UI is really fluid and responsive. All UI transitions and animations are buttery-smooth and we didn't notice any lag. This is hardly a surprise, as the Snapdragon 800 SoC is one of the speedier around.