This starter is annotated reading material and the source of truth for the lab preview. Running anything is optional; the reading goal is to explain the mechanism without hiding behind a framework call.
Practice explaining a parallelism choice with problem, mechanism, communication, tradeoff and measurement.
## Answer template
1. Problem: what does not fit or scale?
2. Mechanism: what is replicated or sharded?
3. Communication: which collective appears?
4. Cost: memory saved versus bandwidth/latency added.
5. Measurement: what profiler or metric confirms it?