Shuttle XPC SB81P: Loaded 775 BTX

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The following components were installed in the Shuttle SB81P:

  • Intel 520 processor (P4-2.8 Prescott, 1Mb cache, 800 MHz FSB in 775 casing), review loan from
  • Samsung SM-352B Combo Drive (CD-RW + DVD-ROM)
  • 256 MB DDRAM - PC2700 generic
  • Seagate Barracuda IV - now out of date, but still a quiet reference drive
  • Microsoft Windows XP Pro SP2 was installed, along with the multi-megs of updates ad nauseum.

    *A note on the Intel 520 processor: Any Prescott-core P4 in a SFF PC is a challenge if you're seeking low noise as a primary goal; they run so very hot that it's hard to cool them in tight spaces without significant airflow. Intel announced several months ago that they were expanding the range of 775 CPUs downward to include lower clock speed Northwood P4s in the mix. We made a special request to to locate one of these for us, but they were unsuccessful. For the record, the 520 is spec'd by Intel for a Thermal Design Power of 84W (and a calculated Maximum Power of 100W), and a maximum casing temperature of 67°C.

You'll note that no video card is listed. Alas, a PCI Express VGA card was not on hand when we were doing our testing, so the integrated VGA was used. Suffice it to say that the noise level of the system cannot be any lower than we recorded here in the absence an outboard VGA card. The only way the baseline noise level can be lowered is by using a quiet notebook drive. However, this noise reduction will be mostly obscured by other sources of noise in the system. We doubt that using a notebook drive in this system would actually improve noise levels by more than ~2 dBA/1m.

The hard drive was installed in the bottom of the drive cage. The secondary drive mounts were not tested.


The SB81P has a good range of user options in the the BIOS.

  • FSB: 100-355 MHz, in 1 MHz increments
  • CPU Voltage: 0.8250-1.5875V in 0.025V increments
  • DDR Voltage: 2.70-2.90V in 0.1V increments
  • Chipset Voltage: 1.60-1.80V in 0.1V increments

The low point for all voltages...

...and the high point.

FSB adjustment range is 100-355 MHz.

We are happy to see that the BIOS allows both underclocking and undervolting to levels well below what is actually achievable. These are particularly important features in a SFF system that may be more of a challenge to silence because of its small stature and its many proprietary parts.


The SB81P allows PWM-regulated control of the CPU and System fans. Each of these categories contains two fans, an intake and an exhaust for the CPU category, and the two 60mm exhaust fans for the System category. The power supply fan is not controllable from the BIOS, and no RPM measurement was shown for it.

Although the CPU fans must be adjusted together, they do not ramp up at the same rate. For most of our testing, the intake fan stayed about 800 RPM slower than the exhaust fan. On the other hand, the system fans are never adjusted independently; they are powered from the same fan header and do not report individual RPM measurements.

Each category can be adjusted between 30% and 100% in 10% increments. Control is achieved though PWM, not straight voltage attenuation. There is also a Smart Fan setting that spins the fans even slower than the 30% setting at idle. All testing was done in Smart Fan mode.

A certain amount of control can be had over the Smart Fan mode via a setting called "CPU Temp Tag". This allows the user to set the CPU temperature at which Smart Fan begins to increase the fans speed. Temp Tag is adjustable between 30°C and 80°C in single degree increments. Since Intel CPUs start throttling at around the 70°C mark, it is actually possible to set the Temp Tag to a temperature that should never be reached. In theory, this means that adventurous users could depend entirely on Intel's CPU throttling technology to cool the CPU without allowing the fans to ramp up.

Fan speeds can be adjusted to a set level between 30% and 100%, or set to "Smart Fan" to allow the BIOS to handle it.

It is possible to set the CPU temperature when Smart Fan kicks in.

One downside of having such powerful fan control in the BIOS is that fan speeds were not controllable via SpeedFan 4.19 in Windows. Aside from this minor gripe, however, we were fairly pleased with the range of adjustment allowed by the SB81P.

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