- 1. Site code (factory of manufacture)
- Encoded in the serial number prefix. Seagate Wuxi (China), Korat (Thailand), and Penang (Malaysia) factories use different head suppliers and slightly different adaptive calibration profiles. A donor from the wrong site can pass initialization and still produce unreadable surfaces.
- 2. Firmware revision (SN/FW pairing)
- Visible via the F3 terminal as the firmware string (for example, SC60, AR13). Mixing firmware revisions across a head swap can shift translator behavior and corrupt the defect list lookup.
- 3. Head map (active heads, not just head count)
- A 14-head Barracuda Pro 10TB may ship with one or two heads flagged dead in the factory head map. The donor must match the original's active head pattern, not just the physical head count. eBay sellers cannot read this.
- 4. Preamp variant
- The preamp chip on the flex cable sets the read channel bias for that specific head stack. Different production batches of the same model number can ship with different preamp parts. The PC-3000 F3 terminal reports preamp signature on attach; a mismatch causes calibration failure before the first user sector is read.
- 5. Platter count and density
- An ST10000DM0004 from one production window may use seven 1.43TB platters; a later revision may use a different platter recipe at the same capacity. The donor head comb spacing and head fly height must match. A mismatched comb scrapes a platter on insertion.
- 6. Manufacture window (date code)
- Two drives with the same model and firmware string can still differ if they were manufactured more than a few months apart. Seagate makes silent revisions to head suppliers and platter coatings within a model lifetime. The date code on the top label and the F3 terminal report must fall inside a window we know to be compatible.