Answer
That four-partition ceiling forces a real design conversation rather than an arbitrary limit. A common pattern is one partition for production, one for test or development, and remaining capacity split between a QA environment and a high-availability replication target, but each additional partition draws from the same four-core IBM i pool, so more partitions usually means smaller, more constrained partitions rather than four fully capable production-sized environments.
Virtual processor allocation is the lever that connects partition count to usable performance. Assigning more virtual processors to one partition can give it better responsiveness under load, but IBM's own guidance notes that doing so may reduce how many partitions can be active at the same time, so the choice is a trade-off rather than a free upgrade. Buyers should work through partition sizing with an IBM i technical resource before finalizing a purchase, mapping actual planned workloads, such as production, test, and DR replication, against the four-core and four-partition limits together, rather than treating the partition count as a simple checklist item separate from performance planning.