Why do fans have two plugs?

Most case fans I've seen, including my own, have two ports like this:
http://vastechnet.co.uk/WebRoot/StoreDaily/Shops/eshop239347/4999/AFD8/7598/F7C2/044F/C0A8/0ADD/DD1B/Cit_80mm_Case_Fan_4_pin_molex.JPG

In that specific picture, I use the bottom plug to connect it to my PSU. But the top plug is unused, what's its purpose?
7 answers Last reply
More about fans plugs
  1. Hmm, never come across that before, none of my fans have that arrangement. But I suspect it's because fans draw very little power it acts like a splitter so you can connect other peripherals via the top molex without the need for tying up more of your psu available cables.
  2. those type of fans are used to connect directly power supply.
  3. xtreme5 said:
    those type of fans are used to connect directly power supply.

    I know that, but there's two plugs, am I right to believe that the other plug is to be able to connect another fan to it?
  4. That's what I suspect it's for, so you can 'daisy chain' them.
  5. Yes, since the fans are plugged directly into the PSU you are able to daisy chain other fans, hard drives, other things with molex connectors.
  6. Keep in mind though the fans will run at the max speed and you won't be able to adjust the speed through software/bios means because the fan is directly connected to the PSU via molex.
  7. Power pass-thru- like other have mentioned, you can run additional molex connections from this.
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