A lot of media depict nobility or even kings living permanently within castles as their main residence. Was this a real practice and if it is was it common or rare?
Yes, medieval nobles lived in castles. The definition of a castle is in fact: a fortified residence, known for the crenelated battlements.
However, in many cases, castles include external walls, some buildings and a central keep - a large stone house/tower. So let’s ask: did Medieval nobility actually lived inside castle keeps as a permanent home?
Well, yes. Sometimes, however, the castle has no keep, and the lord lives in an unfortified house inside the castle wall. Sometimes, their will be a central fortified building, but the lords do not live in this building regularly, only when the castle is attacked. It may be called a Biegfried - a defensive tower not meant to be permanent residence. That means they didn’t have any window, only arrow slits