Why do fans have two plugs?

[GeorgeGeee]

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?

 

[a little black duck]

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.

 

[xtreme5]

those type of fans are used to connect directly power supply.

 

[GeorgeGeee]

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?

 

[a little black duck]

That's what I suspect it's for, so you can 'daisy chain' them.

 

[DarkOutlaw]

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.

 

[junkimchi]

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.

 

[rubix_1011]

Power pass-thru- like other have mentioned, you can run additional molex connections from this.