The PC beta for Battlefield 4 will, interestingly enough, require a 64-bit processor in order to run. That means that unless you're running the game on Windows 7 or Windows 8 64-bit, you won't be able to participate in the beta, as it doesn't come with 32-bit support for whatever reason.
DICE's Technical Director Johan "Repi" Andersson confirmed the detail on Twitter after several users brought the question to his attention.
@szpic_PL yup!
— Johan Andersson (@repi) September 25, 2013
In addition to confirming the detail, Repi added that the beta only has a native 64-bit executable (x64) and not a 32-bit one. The full retail game is expected to support 32-bit operating systems, however.
@TavaFIN yes the beta has only a native 64-bit executable (x64)
— Johan Andersson (@repi) September 25, 2013
With next-gen around the corner, it's easy to see why developers like DICE are utilizing newer (DX11) technology instead of falling back on DX9.