In the ATX case specification, cool air is drawn into a typical case from vents in the front panel. The incoming air helps cool components as it moves through the case, becoming warm in the process. It is evacuated through the PSU and out the rear by the PSU fan. So the loud, fast fans do help to keep a case cooler. Manually varying a high airflow PSU fan can cause CPU temperature to be affected as much as 5-6 degrees C.
The ATX specification was created some years ago at a time when desktop CPUs generated no more than ~30W. Now, they are up over 130W. The airflow arrangement of exhausting hot case air out through the PSU no longer makes as much sense as it did in the past. The PSU has to handle both its own self-generated heat, which is naturally higher than before, as well as the heat generated by the other components.
BTX FORM FACTOR
BTX prototype, mATX equivalent sizeThe various BTX interface, system design and case specifications and studies released by Intel since September 2003 are major departures from the ATX form factor, but they are only just trickiling into the market now from a few vendors. FormFactors.org describes the BTX as follows:
"The BTX form factor specification gives developers options to balance thermal management, acoustics, system performance, and size in the system form factors and stylish designs that are desired in today's products. The BTX form factor is a clear break from previous ATX form factor layouts and was developed with emerging technologies such as Serial ATA, USB 2.0, and PCI Express*.
"Thermal improvements come primarily from taking advantage of in-line airflow. The BTX defined in-line airflow layout allows many of the main board components (i.e.: processor, chipset, and graphics controller) to utilize the same primary fan airflow, thereby reducing the need for, and noise from, additional system fans. In some cases this also allows fewer and/or less expensive heat sinks to be used when compared to ATX solutions. The system level acoustics are also improved by the reduced air turbulence within the in-line airflow system. The BTX layout supports better component placement for back panel I/O controllers — important as the signal speed of external devices continues to increase. In addition to smaller than microATX system sizes, BTX was designed to scale up to tower size systems using the same core layout by increasing the number of system slots included."
We will provide analysis of BTX cases, PSUs and systems as they become more widely available.
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