You might run Roon Bridge and Roon Server on separate hardware for sound quality reasons, depending on the details of your setup.
You shouldn’t have to worry about minimum hardware for Roon Bridge. It is not resource-intensive. Many people run it on Raspberry Pi 2’s and similar devices. You can probably find an ARM CPU that is not fast enough if you look hard enough, but anything Intel-based is going to be more than adequate.
Roon Bridge and Roon Server are software packages. RAAT is a network protocol that streams audio.
Both Roon Bridge and Roon Server expose all of the audio devices on the machine they are running on to Roon as RAAT-based audio zones.
If you’re familiar with AirPlay’s ecosystem, this might help make the relationship clearer: RAAT is to Roon Bridge as AirPlay is to Airfoil Speakers.
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