There is a behavior pattern when hdd head reading user sectors,they occasionally move from the reading area to a fixed area in the center of the platter and then return and continue reading(in sector by sector reading mode not reading fragmented files situation).
Does anyone know what part of the firmware controls this?
Is this s.m.a.r.t?

Are you talking about the parking zone on old drives before ramps were in use?

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Zero Alpha: zeroalpha.com.au
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No,modern hdds with ramp, the heads stop reading and move to the middle of the platter for a split second and then go back and continue reading from the original area.

If this happens at a few sectors repeatably, then probably some servo sector(s) are damaged around the affected LBAs.
It can be head, preamp or PCB related as well, but less likely, and in this case it would happen independent of the LBAs being accessed.

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Adatmentés - Data recovery

In this demonstration, healthy hdd,we see that at any point we want to read information, the read head will move from time to time to a fixed area.
This looks like some kind of service operation performed by the firmware.
If anyone knows how to disable this via the firmware and if we ask to read in a specific area, the read head will focus on the exact area and not move anywhere else,so I will pay for a solution.