Shuttle SN95G5: A64-939 SFF

Complete|Mobile Systems
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CPU Fan Control

Another interesting feature of the BIOS is the CPU Fan Control, which is found under PC Health Status. It has several settings:

  • Ultra Low (1000 rpm)
  • Low (1600 rpm)
  • Mid (2400 rpm)
  • Full (3600 rpm)
  • Smart Fan (~830 rpm default)

Interestingly, the control is selectable between three fan headers: Fan 1, Fan 2, and Fan 3. One last setting selects both Fan 1 and Fan 3. Fan 3 is the header to which the small northbridge HS fan is connected, so Fan 1 + 3 was selected to keep the small fan running more slowly. However, the northbridge HS fan never changed speed, always running 3100~3200 rpm regardless of the fan control setting.

Smart Fan is the most interesting setting. The user chooses a setpoint called the "CPU Temp Tag" from a range of 30 to 60°C. This setpoint is where the CPU fan will begin to ramp up from its minimum speed of ~830 rpm. A chart on the side of the screen indicates the fan's speed setting at specific temperture increases beyond the setpoint.

Note that once the the CPU reaches 80°C, the CPU fan will be spinning at a loud 3600 rpm regardless of which fan speed control setting has been chosen. As an aside, when the fan is running at the top speed of >3600 rpm, it moves a whopping 50 cubic feet per minute. Given that the total volume of the case is less than half a cubic foot, that's enough airflow to exhaust the entire case in half a second! On power up, the CPU fan actually starts at maximum speed for a couple of seconds before slowing down to the BIOS selected speed. How loud was this couple of seconds? Loud: 50 dBA at one meter.


Smart Fan Settings: full throttle at 80°C.


Four settings to choose from.


You get to choose when the CPU fan ramps up!

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