What is the core of Computing? This paper defines the discipline of computing as centered around the notion of modeling, especially those models that are automatable and automatically manipulable. We argue that this central idea crucially connects models with languages and machines rather than focusing on and around computational artifacts, and that it admits a very broad set of fields while still distinguishing the discipline from mathematics, engineering and science. The resulting computational curriculum focuses on modeling, scales and limits, simulation, abstraction, and automation as key components of a computationalist mindset.