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  Intel's BTX form factor, with a B for better? 
  Jan 26, 2005, 08:30am EST 
By: Sander Sassen

We reported on Intel’s new form factor, BTX, a while ago with the promise to investigate things further when actual BTX products were available. Well, we’ve just been handed a AOpen B300 micro-BTX case, an Intel i915 chipset micro-BTX motherboard and supporting processor heatsink kit a few days ago and we set to work to evaluate it. The motherboard and case we’ve been sent supports the new micro-BTX form factor which, in terms of motherboard size, is comparable to micro-ATX. As mentioned in our previous article the BTX standard defines a new layout for the motherboard where the two major contributors to raising the case temperature, the processor and graphic card, have direct airflow over them.

The processor’s heatsink is placed in an air duct which draws cold air from outside of the case directly in, without being hampered by any obstructions. This air duct is part of the BTX case and its location and size adhere to strict specifications, as does the location of the processor socket on the motherboard. All other components such as the power connector, memory and expansion slots also have a set location on the motherboard, thus allowing a BTX case and motherboard to be tailored to each other’s needs exactly. Because of this efficient use of space, BTX cases can be smaller than ATX cases, as they make optimum use of the available space, but, due to the optimized airflow, run cooler than ATX.

Micro-BTX case front

Micro-BTX case fan duct

Fan size compared to 80mm fan

A look at the front of the micro-BTX case, the fan duct and the size of the fan.

As you can see from the images the ducted heatsink lines up with all of the other components that need to be cooled and as such provides airflow over the processor and all other devices. With ATX many components needed to have their own forced air cooling, chipsets for example, simply because there was no airflow over them from the processor cooler. With BTX we can suffice with a simple passive heatsink, placed in the airflow of the air duct, which obviously cuts down on noise production. Video cards also can be placed directly into this airflow, allowing them to be cooled more efficiently.

The size of the fan mounted in the fan duct is considerable, 92-mm and has a fan blade configuration that allows for wider more angled blades creating strong airflow whilst remaining reasonably quiet. As can be seen from above image it dwarfs an 80-mm case fan which is often used to provide additional airflow in ATX cases. On top of that the fan is temperature controlled by a built in thermistor and is further regulated by another thermistor that sits right behind the fan duct in the airflow. This combination of one thermistor measuring the outside air temperature drawn in by the fan, and another right behind the fan duct measuring the temperature after the air has passed over the processor heatsink causes for an efficient means of controlling noise and cooling performance.

Micro-BTX, all components mounted

Micro-BTX, case opened

Micro-BTX, case rear view

A look at the inside with the case opened and a rear view from the case.

There are a few drawbacks about this approach as well, components will be cooled with airflow coming from the processor heatsink, thus the temperature will always be several degrees higher due to the heat dissipated by the processor. But there’s more; due to the small size of the micro-BTX case the power supply and harddisk are tucked away in a corner with very little or, in case of the harddisk, no airflow over them at all. This means that under heavy loads the power supply fan will need to spin up to a high rpm to provide adequate airflow to keep it cool. The harddisk will not receive any cooling, but for natural convection, which, with today’s 200GB and larger harddisks, is not recommended, temperatures will rise quickly and cut into the MTBF of the harddisk. In terms of noise production, which is highly subjective, the micro-BTX case fared well. It isn’t exactly whisper quiet, but with the notion that there’s a 3.6GHz Pentium 4 processor running inside that small case it bests any other small case we’ve seen thus far. Due to the fiery Prescott core it is hard to properly cool these processors in a small case and keep quiet about it, this micro-BTX case with ducted fan heatsink certainly is up to the task.

PCIe bracket for full size card

PCIe video card mounted

The supplied PCIe bracket and a full-size PCIe video card mounted into the case.

So to summarize our findings we can honestly say that the ducted fan heatsink does a good job of keeping the Pentium 4 processor running cool, but also quiet. We’re not that enthusiastic about the mounting of the harddisk and the restricted airflow over the power supply though, as both these components are major contributors to system noise and increases in case temperatures. Nor are we especially pleased with the case temperature as that was on average several degrees higher due to the air being passed over the hot processor heatsink before entering the case as a micro-ATX case of similar size. But overall the micro-BTX system left a good impression; it is quiet and has a small footprint, smaller than most micro-ATX systems. And unlike a micro-ATX system running a Pentium 4 processor it runs quiet enough to be used in an office environment for many hours a day. For the enthusiast wanting to have more than a single harddisk or single optical drive mounted this micro-BTX case is not well suited, nor will it accept video cards such as NVIDIA’s GeForce 6800 or ATI’s X800 series, as these simply will not fit, but it will do fine as a small office or home PC.

Sander Sassen.

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