Shuttle XPC SB81P: Loaded 775 BTX

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Removing the cover of the system reveals quite a different layout than other Shuttle systems we've looked at. The changes reflect a shift towards BTX design.

  • The power supply is a more conventional shape, and is located at the back of the case. Previous Shuttle designs used elongated power supplies mounted along the side of the case.
  • The CPU is located at the front of the system rather than the back.
  • The PCI slots are on the "wrong" side.
  • There is room to mount two 3.5" hard drives at the top of the case. The case has room for a total of three 3.5" drives, including a floppy if needed.

A top down view reveals a block-shaped power supply and PCI slots on the "wrong"right side.

The reverse view. There is room for two hard drives to sit across the width of the case at the top, one after the after.

The power supply's blocky shape should be better for internal airflow.


The move to a more conventional PSU shape is dictated partly by Shuttle's preparation for BTX, and by the need for greater power capacity. The long and slim 40mm fan cooled PSU used in recent Shuttles probably cannot be cooled adequately enough to deliver any more power than they were already squeezing from it. The more conventional 80mm fan should do a better job exhausting internal heat and any heat generated by the VGA card.

Shuttle SB81P Power Supply, Model PC43I3503
AC Input
100 - 240 VAC, 50-60 Hz
DC Output
+12Vsb A
+12Vsb B
Max Power
Total Power

The specifications for the power supply are unusual. Most puzzling are the complete absence of the -12V and +5Vsb rails. Initially, it looked like an error in the specs, but an examination of the output wires proved them to be correct. The power connectors (yes, plural) for the motherboard are proprietary. A 6-pin connector with three 12V-neutral pairs (like a PCIe connector) appears to supply the power for the CPU. Another 8-pin connector with three more 12V-neutral pairs, a ground, and a power-enable pin presumably supplies power to the rest of the board. A further power header for a 4-pin floppy connector is also on the motherboard but was not used in our sample. No documentation for this extra header could be found.

Most of the power appears to be drawn from the two +12Vsb lines. It is probably safe to assume that each of the power connectors on the motherboard has its own +12Vsb line. Each line is rated for 204 watts, enough power for the hottest CPUs and GPUs on the market today with a fair amount of overhead.

One thing that is unclear about the +12Vsb lines is whether they are active while the power supply is off. Ordinarily, "sb" stands for standby, which means power is supplied on this rail even when the system is off. Presumably, the power to the CPU and GPU is switched on the motherboard itself if these lines are indeed active whenever the power supply is plugged in.

To make room for the large capacity +12Vsb lines, the remaining rails are quite stunted in comparison. The +3.3V, +5V, and +12V lines provide just enough power to spin up any drives that are installed.

No testing was performed on the power supply. Assuming that it is rated accurately, it should provide ample power for any system that can be assembled in the small confines of this system. Efficiency of the power supply is unknown, and therefore so is the heat it contributes to the system.


Intel's LGA775 socket was designed with the BTX form factor in mind, so it is no surprise that Shuttle's first socket 775 system sports a BTX-style "thermal module". The main idea is to cool the CPU with fresh air ducted in from outside the case. The SB81P achieves this by ducting air across the motherboard; air enters the duct at the front right of the case and warm air is exhausted from the front left.

The CPU socket has been moved to the front of the case.

The CPU duct takes up the bottom corner at the front of the case.

While the thermal benefits of this CPU duct are quite clear, it is somewhat uncertain how this change in design will affect noise levels. It is unlikely that moving the CPU from the back of the case to the front — closer to the user — can be a good change acoustically.

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