I'd like some info on people who have the quiet PCs. The PCs that have "smart fans" that run at reduced RPM when not needed.

I just bought system that shows BIOS controls for two "smart fans" in the BIOS manual.

I only have one "smart enable/disable" control in my actual PC BIOS setup.
Is the reason I only have one smart fan control the fact that I don't have the right fan for the case.

When I connected an 3wire fan, it displayed RPM in the BIOS but no smart control to change or limit speeds.

Does your machine have two "smart fan" controls, what fans are you using?

Does the BIOS manual provide any additional information regarding how the control functions??

My ASUS motherboard monitors RPMs in the BIOS. Until now, my understanding of "smart fans" was in regard to their ability to alter RPMs based on CPU or case temperature due to a "heat sensor" (thermistor) built into the fan assembly...

One thing I did happen upon was some motherboards are apparently capable of adjusting the core voltage to the CPU in conjunction with a "smart fan."

What motherboard do you have?

Right, I have Asus and Soyo boards that display rpm in the BIOS for both system and cpu fans. And I believe that most of the mainboards must have their own thermister, [at least the cpu has "somekind" of thermal circuit]

For instance, I pulled the wire on my Biostar's Athon cpu and watch the temp climb in the BIOS display (the fan wasn't providing temp)

I emailed BIOSTAR about the "BIOS screenshot" that shows two different smart controls. [My BIOS only has one] I figure, they muffed a connection somewhere on one of the board revisions so "temp signaling" is only working for CPU not the chipset area on the board. Theres a pretty hefty heatsink on the mainboard but Sandra keeps reporting the board to be 176F .... they admit, they esitmate board temp off a formula. But I figure the reading is a result of scrambled data at whatever SMB address space responsible for the temp reading, the same reason ther'es no "smart sense" system fan control on my board........scrambled relationship between the BIOS address space for the reading and the actual board bus.

Maybe that's why these boards are dirt cheap $52 retail, $38, oem pricing.

My guess for the price of the boards is that they aren't the advanced type that adjust the core voltages based on heat.

My hunch is also that the "smart fan" monitoring is probably just RPM monitoring...

Well, your remark about the "thermistor" being in the fan makes sense.

Two different signals do exist however, a thermistor by design will change a voltage by temperature in a simple circuit. But it takes another chip, or IC to do the rpm counting. Any yet another function,is needed to report the CPU changing temp as the system is turned on, with the fan entirely disconnected.
(I have tested and checked BIOS temp report with fan dissconnected)

So what I know: Temp sensing circuit exists for CPU, and reports to BIOS correctly. RPM sensing circuit exists and works correctly for both fans connected.

Sandra utility reports high board temp (scrambled data?) no CPU temp, but does report system fan failure if dissconnected.....

I have fans in my case with a thermistor that can be positioned independently. I also have a Thermaltake CPU fan with a thermistor that resides beneath the CPU. Its connections allow me to use the thermistor to control fan speed via heat, or connect a small potentiometer to regulate the speed as I see fit.

My ASUS motherboard has two embeded thermistors that monitor CPU temp and also motherboard temp...

So, it appears that we are capable of collecting similar data...

What I'm trying to figure out is what the "smart fan" hype is all about...

My setup appears to be similar to the motherboards you have. My Thermaltake case fan and CPU fan are advertised as "smart fans," and although they report RPMs picked up by the BIOS via the motherboard headers, their speed is controlled independently of the motherboard by their own internal thermistors...

I'm trying to figure out if the "smart fan" technology they are hyping allows the motherboard to control fan speed directly through its embeded thermistors??

So what I know: Temp sensing circuit exists for CPU, and reports to BIOS correctly. RPM sensing circuit exists and works correctly for both fans connected.

Unless there's something we're we're missing, the fan headers are simply reporting RPMs but have no capability to control fan speeds. These are similar to the ones I use:

http://www.thermaltake.com/dcfans/smartfan/a1357.htm

Here's an interesting read on what the motherboard "smart fan" technology apparently is supposed to do:

http://www.silentpcreview.com/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=64&page=1

It appears that any three lead (RPM sensing) fan would work (sans a thermistor like the Thermaltake fans I have in use on mine).

Voltage/fan speed is controlled through the fan headers via the embeded motherboard thermistor...

It didn't appear that your BIOS setting allowed any control as in the article???

Just a comment: One of the forum members here, Rick, counseled me when I first got into computer building to use the motherboard fan headers for sensing only due to the potential strain of putting 12v through the headers.

My 12v fans are connected to the motherboard fan headers via the RPM sensing leads only and 12v adapter plugs are used to carry power directly from the power supply 12v rail.

Rick's logic still makes sense to me when considering 12v (car battery voltage) is being pushed through the copper traces on the motherboard to the fan headers...

Hey, thanks to you, and to the other forum members who pointed me the MBM utility.

First off- the learning curve on this kind of crap completely sucks........

Here's what's going...... There are chipsets, that control the "enviroment functions" for the mainboard and CPU. In my case, the chipset is ITE8712-A.

My board isn't listed in the MBM utility, but hell that wouldn't stop me, So I manually plugged in a board that uses the "ITE8712" chipset. (note not the "A" version")

After much mucking around, and too much time-wasting, I have discovered that this board is indeed buggy in at least one respect. If you look closely, it originally had an additional fan-header that was removed. (visual on board)

Anyway, with the MBM utility, I deduced that the CPU fan header/sensor does correctly sense RPM and temp. And that the mainboard sensor, near PCI slot 1, will report RPM changes but goes "flat out" reporting high temp...... just like Sandra.....

THe MBM utility let me confirm dual sensors and locations by trial and error.

Of some note, the PSU fan is indeed being regulated, but I don't know if it is by mainboard sensor, or by fan-body sensor. (I assume fan-body) [because temp signal is flat out form board]

Google search has confirmed other investigations, and temp/sensor reading abnormalities for the ITE8712-A IC. (other board manufactuers)

I'm not to worried or pissed about board or system, just how long it took me to get to the bottom of this.

Thanks for the links, I still have much to learn, and maybe I'm wrong about all this too..

PS - It's no coincidence that BIOSTAR doesn't have a working mainboard utility for this board, like they have for almost all their other boards......the joke's on me.