Windows RT was largely unmentioned during Microsoft's Build opening keynote on Wednesday, but the company is also releasing a preview version of Windows RT 8.1 this week. Designed to update ARM-based tablets to the same features that Windows 8.1 provides, there's little difference between the two. I got the chance to run Windows RT 8.1 on a Surface RT and see exactly what Microsoft has improved.

First things first, the desktop mode remains. Despite not being able to install and run traditional desktop applications, the desktop mode in Windows RT 8.1 is still present and includes the Start button just like its x86 counterpart. It's not that surprising given Microsoft's stance with Windows RT, but it's clear the company is continuing to develop both operating systems alongside each other.

Desktop remains, alongside some small performance improvements

One of the big drawbacks to Windows RT devices has been performance. During our initial review of the Surface RT we noted that apps were slow to load and it was occasionally laggy, but Microsoft has been working hard over the last seven months to improve things. Monthly updates have made the Surface RT more speedy, but Windows RT 8.1 doesn't appear to improve things dramatically. It feels a little smoother in certain areas, but loading apps is still painfully slow. Launching Xbox Music, which has traditionally been laggy and cumbersome on Windows RT, was particularly slow with elements taking their time to load.

With the Surface RT you can snap two apps side-by-side, and improvements to the Live Tiles and UI are all present. On the device we were testing Office wasn't available, but Microsoft assures us that those upgrading will continue to be able to access the desktop Office apps as normal on RT devices. Windows RT 8.1 also includes an Outlook RT desktop application, but we were unable to test this initially. The company also announced it's building Windows 8-style "Metro" versions of Office today, and they're expected to debut later this year.

Overall Windows RT 8.1 is an identical counterpart to the x86, and that's both a good thing and somewhat disappointing. Thankfully, Microsoft has done a lot of work to improve the PC settings in Windows RT 8.1 to ensure you don't have to switch into the desktop mode as much. This finger-friendly approach is an improvement for these ARM-based devices, but the fact the desktop mode remains — without a lot of functionality — is still puzzling when the majority of apps will run in the "Metro" mode on Windows RT 8.1.