If your writing a "Windows Store" app, then your app will run in Windows RT (aka Windows on ARM) as well as Windows on Intel/x86 (aka "Wintel").
If you're writing in C or C++, you will have to deploy two packages. Any other language (C#, VB, JavaScript) will require only one package.
Thanks,
Frank | Developer Evangelist @Microsoft
http://bit.ly/30ToLaunchWin8[
^]