How/Where the partitions created before assigned to devices

This might be a silly question. When creating a ring, the ring actually is assigning, for instance, num_device*100 partitions to each ring. the num_device*100 partitions, they aren't physical partitions, right? Where they get created and How?

If I have 5 device with same weight, and each has 1TB. if i set power_count as 18. so all devices will get 2**18 partitions, each partition has the same size which is 1TB*5/2**18?

Initially, each partition will have none index, until ring starts put path's MD5 hash index against them to kinda activate them?