Intel® Boxed Processor thermal solution overview
As processor power has increased, required thermal solutions have generated more noise. Intel has added an option to the boxed processor that allows system integrators to have a quieter system in the most common usage.
Older generation boxed Intel fan heatsinks contain built-in circuitry to control fan speed. They had a thermistor in the fan hub which measured the chassis ambient air temperature. The fan circuitry then adjusts the fan speed to properly cool the processor at the slowest speed allowable. If the chassis ambient temperature is cool, then the fan will run slower and quieter. If the ambient temperature is hot, the fan will run faster.
This fan had to work in a variety of operating conditions so it had to be designed in such a way that it would cool the processor when running at its maximum power at any given ambient temperature (up to 38°C). In normal operating environments, the processor rarely reaches its maximum power rating.
Under most conditions the fan is spinning faster and louder than necessary. (The fan heatsink is required to work this way so that it will properly cool the CPU in all specified operating environments.)
Intel has been aware of customer concerns over increasing fan noise. Intel has now designed a fan speed control technology to take advantage of the fact that the processor is not always running at its maximum power. This was done by basing the fan speed control on actual CPU temperature and power usage.
The speed of the new fan heatsink is controlled by the additional 4th wire of the fan cable. ("4-wire fan speed control.")
The additional 4th wire sends a signal from the motherboard to the fan heatsink to control its speed. There is a digital thermal sensor in the processor which measures actual CPU temperature. The processor sends information to the motherboard about its specific thermal requirements and the actual processor temperature. The motherboard then uses this information to optimally control the speed of the processor fan.
Figure 2 shows the current fan speed curve (red) of a 3-wire, fan heatsink-thermistor based fan speed control. The additional curves in blue represent fan operations at lower CPU temperature and power consumption levels based on the 4-wire fan speed control fan heatsink.
Figure 2. Internal chassis temperature effect on boxed processor variable speed fan heatsink noise
The "Max Temp" in Figure 2 represents the upper set point or worst case ambient temperature of 38°C. The "Min Temp" represents the lower set point or the slowest possible fan speed at an ambient temperature of 30°C. (See Table 1)
The acoustic benefits of the 4-wire based fan speed control may vary depending on the specific motherboard implementation. (The acoustic benefits are reliant on the motherboard implementation of fan speed control.)
Intel has developed a motherboard based fan speed control called Intel® Quiet System Technology (Intel® QST). This new technology uses a PID controller that can measure the rate of change of the processor temperature, thus predicting when the processor will reach its maximum temperature. If implemented correctly by the motherboard manufacturer, the control algorithm will operate the processor fan at minimum speed under most operating conditions. Since Intel® QST can predict when the processor will reach its maximum temperature, it will delay increasing the fan speed until just the right moment in order to keep the processor from exceeding its maximum temperature. Consult your motherboard manufacturer to see which motherboards they offer with support for Intel QST.
A 4-wire fan does not guarantee a quieter system. If the processor is being used in a hot environment and is under heavy loads, the fan will have to run fast enough to properly cool the processor. The internal chassis temperature is required to be maintained at 38°C (or lower). Selecting the correct chassis (see Chassis Selection) and verifying proper thermal management is critical for integrating a high quality Boxed Intel® Core™ i7 Processor-based system.
Table 1. Boxed processor variable fan heatsink set points
1 Set point variance is approximately ±1°C from fan heatsink to fan heatsink.
|For Boxed Intel® Core™ i7 Processors in the 1336-land package|
|Internal Chassis Temperature (°C)
||Boxed Processor Fan Heatsink Set Points|
|X <= 301,2
||Lower set point: Fan speed constant at lowest fan speed. Recommended temperature for nominal operating environment.|
|Y = 35
||Recommended maximum internal chassis temperature for Boxed Intel® Core™2 Quad Processor-based systems.|
|Z >= 391,2
||Higher set point: Fan speed constant at highest fan speed.|
2 Intel® Core™ i7-965/975 Processor Extreme Edition do not use a thermistor so upper and lower set points are not relevant.
Figure 3. Processor box label