I have 4 HDDs here with me, from 3 different manufacturers, and all of them have the following 4-pin extra interface beside the SATA connector:
HDD with 4-pin interface
Looking on the internet, I can see that it exists on all HDD devices, but not on SSDs:
SSD without 4-pin interface
On old IDE devices, there was a similar interface used to select operational mode (master/slave), but on SATA it doesn't make sense anymore.
Could someone tell me what this interface is intended to do and why it doesn't exist on SSDs? It is used in any practical situations?