Rare and expensive elements aren't only found on the platter, as we'll see when we look at that other important part of a hard disk drive - the read/write head.
Those, and the current sector number virtually rotating under the emulated read/write head, are tracked by the emulator in order to determine which sector is to be accessed.
The new data blocks are necessarily scattered, slowing access due to seek time and rotational latency of the read/write head, and incurring additional overhead to manage additional locations.
Embedded servo systems embed the feedback signals for the read/write head positioner (usually a voice coil motor) inside gaps ("wedges") in the data tracks of the disk.