Need advice on fan connections for first computer build

buildpcjd

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Feb 7, 2016
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I've been getting advice over here...
https://www.reddit.com/r/buildapc/comments/4mctja/help_me_build_my_pc_from_parts/

No comments on this thread though. That's my question. Same question for here.
https://www.reddit.com/r/buildapc/comments/4qfgww/questions_about_connecting_fans/

I've got my heatsink fan plugged into the mobo cpufan1 connection. No problems.

I'd rather have the OS/BIOS control the two case fans (one in front, one in back), so I don't need to use the tower cables that allow a switch up front to physically control low-med-high fan settings on those fans.

I'm wondering about connecting the two case fans to the mobo though. The mobo connections for systemfan1 and 2 have four pins. My case fans have three pins. Is it safe to plug a 3-pin case fan into a 4-pin mobo connection. Here's a pic of how I've got it set up now.
http://imgur.com/fppgjhp

Is that ok? Is it safe?
 

buildpcjd

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Feb 7, 2016
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4,510
Thanks. What's PWM?

Is there any site (or anyone here want to?) that explains the differences between 2, 3, and 4 pin fan connections?

2 is just on/off?
3 is on/off and low-med-high control? Or just having more control over the speed of the fan?
4 I just hadn't seen before.
 
1) Black = Ground
2) Red = 12v
3) Yellow = RPM sensor
4) Blue = PWM RPM control.

Colors aren't exactly standard, but pretty much.

CPU fans generally have 4 pins because their speed is actively controlled.

other fans generally have 3 pins because their speed is controlled by reduction in voltage via motherboard or fan controller.