I just read that there will be two versions of Windows available: Windows RT and Windows 8.

Could someone please describe what the differences between Windows RT and Windows 8 are? And how these differences may affect developers creating apps for one or the other?

Also, what is WinRT?

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    I'm voting to close this question as off-topic because it's not about software engineering or conceptual questions about software design.
    – Andres F.
    Nov 15 '16 at 19:41
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    I vote to close because it's incredibly outdated. Things and namings have changed so much, in windows world, this question can only introduce more confusion.
    – ZJR
    Nov 15 '16 at 19:45

In Brief...

  • WinRT (Windows Runtime, unlikely to be what you meant) is a software layer on top of which Metro apps are built, while Windows 8 is the whole operating system;
  • Windows RT (most likely the one you meant), this is a version of Windows 8 for devices using processors based on the ARM achitecture and instruction set.

You got the names a bit mixed up apparently - granted they made them confusingly similar - so I just addressed both and edited your question accordingly.

WinRT / Windows Runtime

WinRT a software layer that sits on top of the OS, and that is at the base of the new Metro design language approach. It's primarily a set of APIs to build Metro apps for all Metro-supported platforms (including for Windows 8 for ARM).

See the image below for a general approximation of the Windows 8 Platform:

Windows 8 Platform

Windows RT / Windows 8 for ARM

Windows RT (where RT also means "runtime", to make things as confused as possible), used to be known as Windows 8 for ARM. It is a version targeting hardware manufacturers (mostly aiming at the tablet market).

See this post Announcing the Windows 8 Editions (Archived, July 2012) of the Windows Team's Blogging Windows blog (emphasis mine):

Windows RT is the newest member of the Windows family – also known as Windows on ARM or WOA, as we’ve referred to it previously. This single edition will only be available pre-installed on PCs and tablets powered by ARM processors and will help enable new thin and lightweight form factors with impressive battery life. Windows RT will include touch-optimized desktop versions of the new Microsoft Word, Excel, PowerPoint, and OneNote. For new apps, the focus for Windows RT is development on the new Windows runtime, or WinRT, which we unveiled in September and forms the foundation of a new generation of cloud-enabled, touch-enabled, web-connected apps of all kinds.

See the original post for a table listing the major differences between the versions, or Wikipedia's Windows 8 Editions article for more details and sources.

Note that only software written using Win RT (the APIs) can run on Windows RT (the OS version).

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    Not to mention, Metro UI = Modern UI = Windows Store App ≅ WinRT app. I've always been a strong critic of Microsoft's ridiculous naming changes, and they've been burnt really bad in the past. They never learn. Nov 8 '12 at 2:50
  • @ReiMiyasaka: yeah.. like Orcas and Orca Aug 19 '15 at 20:24

Windows RT vs. WinRT vs. Windows 8!!

One of the things that I was confused about in the last few hours, and I am confident that many more people are going to be confused about in next few months is the difference between “Windows RT” and WinRT. Here is the simple version:

Windows RT:

  1. It’s an OS.
  2. It’s a variation of the Windows 8 OS that Microsoft has specifically designed for devices running ARM devices.
  3. (In case you are wondering) ARM is an architecture used by many processor companies to design their chips, including Qualcomm, nVidia, Texas Instruments and several others.

What that means is that when you go to the Settings -> PC Info screen of a tablet device running an ARM processor, it will show you “Windows RT” and NOT “Windows 8″. So, it’s a full-fledged OS that is branded and sold separately by Microsoft to tablet OEMs (aka manufacturers) who are using ARM processors in their tablet devices. In fact, it used to be called as “Windows on ARM” earlier but was later on re-branded as Windows RT.


  1. it’s a runtime.
  2. Conceptually, it’s not very different from .net, java or any other runtime in the sense that its main goal is to create a cross-platform application architecture on Windows 8 that supports multiple languages (C++, C#, JavaScript, etc.).

Difference between “Windows RT” and “Windows 8“:

Now that we know that Windows RT is an OS, I am sure that some of you are wondering how it is different from Windows 8. Here it is!!

  1. Not much different from user experience point of view as both support Metro/Modern UI.

  2. Windows RT is not sold directly to consumers, and is meant only to be sold to device manufacturers (aka OEMs).

  3. The goal behind Windows RT is to give end users consistent experience across tablets being offered by various manufacturers (including Microsoft’s own device called as Surface).

  4. Windows RT will come pre-packaged with MS Office, whereas Windows 8 users will have to buy (and install) Office separately.

  5. There are similar differences in terms of applications shipped out of the box in Windows RT and Winodws 8, as well as the kinds of applications you can develop/install/uninstall on them. Windows RT seems to be more locked-down version of the two.

  6. You also cannot use Win32 and COM APIs on Windows RT, so you are pretty much restricted to using WinRT APIs. Although, over next few days I am going to be closely working on a project that requires access to underlying System Information on a Windows RT “ARM” device. It seems that there may be a way to access a subset of Win 32 API on a Windows RT device. If it works, I will post my experience in a subsequent post.

    If you need any other question please post here itself

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    If you access Win32 dll files then you won't be able to publish the software on the Windows Store. Besides only certain Win32 dll files were made to support Windows RT.
    – Ramhound
    Sep 14 '12 at 13:20
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    How does Windows Phone 8 fit into the mix? That is, does it accept more APIs than RT? My impression is that it does. <sub>(AIA for zombie questioning, but following "please post here itself" request.)</sub>
    – ruffin
    Aug 24 '15 at 14:00

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