Consumer hard disks such as the ST8000DM004 are abundant in the studio due to the low cost / GB. The average selling price has fallen somewhat and Seagate is mass producing them.
The ST8000DM004 is a standard 4 plate assembly using 2 TB per platter. For the most part these disks are fine for general purpose storage on a PC. The only real gripe is that they are slow to copy large amounts of data around.
The Toshiba 12 TB is an enterprise class hard disk that is a universe better than the ST8000DM004. The cost per GB is not as bad with Toshiba so their disks are popular with consumers.
Enterprise class hard disks are 9 plate assemblies with a helium pack to reduce friction. This design is likely to be mainstream before long primarily due to the ability to pack 9 plates in a standard desktop disk case. Lower prices for this class of disk has make them popular with NAS users.
The 18 TB disk is the main capacity for enterprise class disks. Efforts to get to 20 TB and larger capacity points are pushing areal density. On idea is to squeeze in 10 plates into the assembly to reach 20TB.
As the bit areas become smaller, with areal densities beyond 1.2 Tb/in2, binary value becomes harder and harder to read, and bits can reverse. Two factors for magnetic storage to consider, coercivity and retentivity. This is driving the use of heat assisted writes to improve coercivity.
Seagate has been sampling the heat assisted disks now for about a year. So far there has been no comments on disk survival which is important in data centers. Now Seagate is developing their second generation of heat assisted drives which may surface in 2022 given the pace of change in the industry lately.
At present it does not appear that hard disk vendors are going to be able to improve the number of tracks per inch easily. Iron platinum alloy magnetic films to scale to 4 ~ 6 Tb/in2 in areal density but thermal writes are needed to handle the higher demands of the alloy. Careful annealing of the iron platinum alloy is needed to be able to reach close to 100TB.
Eventually, somebody will figure out a way to make 30TB hard disks. 50TB are not far fetched but past 90TB the iron platinum alloy starts to lose the race to 1PB. Research to find new alloys is ongoing.