1. Am I correct in understanding that no SATA hardrive needs 3.3V for "basic" (identification/read/write) operations?
  2. Should a drive have 3.3V specs written on its front along with 5V and 12V if it uses 3.3V? (I don't recall seeing 3.3V specs on harddrives myself, but maybe my drives are not that modern)


I'm investigating glitches on my PC. Working hypothesis is failing old PSU. I'm trying different connections of power peripherals. I've connected one SATA harddrive with Molex-SATA adapter I see errors at Linux boot time. I'd like to rule out MOLEX factor.


3.3 V is supplied along with the traditional 5 V and 12 V supplies. However, very few drives actually use it, so they may be powered from a four-pin Molex connector with an adapter.

The new Power Disable feature (similar to the SAS Power Disable feature) uses Pin 3 of the SATA power connector. Some legacy power supplies that provide 3.3 V power on Pin 3 would force drives with Power Disable feature to get stuck in a hard reset condition preventing them from spinning up. The problem can usually be eliminated by using a simple “Molex to SATA” power adaptor to supply power to these drives.

Here is also about it: https://www.reddit.com/r/DataHoarder/comments/7fx0i0/wd_easystore_8tb_compendium/

The issue as the HGST document explains is that P3 (Pin 3) functionality was re-defined for SAS spec, and then later it was pushed into SATA Rev 3.3.

Q: When was this feature introduced on SAS HDDs?

A: With the introduction of 12G SAS, a new SAS standard, SAS-3, redefined P3 (Pin 3) from “3.3V Power” to “POWER DISABLE”, i.e. “Reset”. At that time, the STA (SCSI Trade Association) researched the marketplace and determined that there were no conflicting legacy concerns.

It was known that there could be legacy compatibility issues. It seems this re-defined P3 spec was pushed on manufacturers by datacenter owners that wanted to save money from having a tech forced to manually pull and reseat a specific drive (reset) under limited cases of drive lockups.


1 Answer 1


Some older drives that meet older sata specs may actually use 3.3V. Some or many may not need it.

Yes, if they need 3.3V, then they should list that on the label. Whether they do or not is up to the manufacturer. It's bad policy to require a voltage not listed but it happens.

Only way to tell if it needs it is to omit it and it fails, include it and it doesn't. Or check what revision of sata it conforms to, by the label or by an online search.

  • \$\begingroup\$ Thanks. I hope so. Just came to my mind, a related question: current (amperes) on the label are max or average or...? \$\endgroup\$ Jan 16 at 5:08
  • \$\begingroup\$ @Martian AFAIK if tends to be average. Surge current is not represented. \$\endgroup\$
    – Passerby
    Jan 16 at 5:47

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