Before any of the technology makes sense, it helps to know who is actually in the room. An AI data centre is not built by one company. A typical deployment involves an organisation that sells the compute, a different one that owns the building, several that manufacture the hardware, and at least one that assembles all of it into something that works. They have different commercial incentives, different timescales, and different definitions of "done".

This chapter uses a four-tier model to introduce them. Treat it as a way in, not as a classification to defend: several major companies sit in more than one tier, and the explorer below shows how the relationships actually run.