BTX is a family of PC motherboards announced by Intel in the Fall of 2004. BTX motherboards are designed to achieve better heat management than ATX motherboards with fewer fans. The most obvious change is that BTX motherboards and their cases are mirror images of ATX with the Power supplies and drive bays on the left side of the case rather than the right as in older (PC, AT, ATX designs). Card slots are on the right rather than the left. This probably precludes installing BTX boards in older cases, or designing cases that will accept both ATX and BTX boards.

Other changes entail moving and reorienting high heat components (CPU, Northbridge, Southbridge chips) for improved heatflow and rearranging connectors. The CPU heatsink has become a "Thermal Module" which will come in at least two configurations. There are only two fans in the BTX arrangement -- one on the CPU, the other in the Power Supply. Airflow is from the back of the case to the front with air reaching the CPU last after drawing heat from other components first. Because the thermal module form factor is defined and the CPU location is fixed, the thermal module can fit into a rubber bezel that ensures that outgoing air is actually vented outside the case rather than simply being reflected into the case..

Preliminary tests show BTX motherboards to be quieter than ATX -- presumably because they have fewer fans -- with heat more evenly distributed. Component temperatures are comparable to ATX.

Drawbacks include awkward cable placement and the fact that maintenance access to the power header on the motherboard, and memory is likely to be blocked by the drive bays.

Three physical sizes have been defined for BTX -- standard BTX, microBTX and picoBTX

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