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

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

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?

3 Answers 3


Those are jumper settings, similar to the IDE drives you mention, but for SATA specific options depending on the drive maker. For example, on this Western Digital support page for mobile drives, it shows two options:

enter image description here

Also, it doesn't exists on SSDs because there is no spinup or spread spectrum related to solid-state devices.

@Adrian Cox mentions in the comments below, a different pin function for Seagate drives.

  • 22
    > RPS: Used by external hard disks to reduce spinup current and allows it to work over USB interface. I am going to punch you! Why didn't you post this a couple of months ago, before I rigged a SATA drive with a DIY-external-drive setup (eBay cable and power adapter)? Maybe then it would not have (literally) burned out the PCB. :-( +1 for both answering the question and enlightening me on about RPS.
    – Synetech
    Jun 26, 2012 at 19:18
  • 5
    Presumably its lower performance than the full power spin up. I wouldn't be surprised if the drive ran at a slower RPM as well.
    – Journeyman Geek
    Jun 27, 2012 at 0:20
  • 3
    @kayEss As USB ports are designed to work with 500mA max, if you start a HDD with 1A it will burn...
    – Diogo
    Jun 27, 2012 at 2:10
  • 17
    You should probably emphasise that the jumpers are manufacturer specific. For instance, Seagate have the same four pin connector, but with a different function: knowledge.seagate.com/articles/en_US/FAQ/193991en
    – Adrian Cox
    Jun 27, 2012 at 7:55
  • 4
    Seagate moved their page from @AdrianCox answer. wayback has it though web.archive.org/web/20160608230214/http://knowledge.seagate.com/…
    – dgrogan
    Jul 21, 2019 at 20:15

According to what i can find its a Manufacture specific firmware terminal that aids in HDD recovery. PC USB Terminal adapter There's a few images on this particular page that shows how to connect a USB cable to those ports using Manufacture specific adapters.


That's a temperature port compatible for imac

  • Although this might be a right response, but this is not the right answer.
    – thethiny
    Dec 30, 2020 at 13:23

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