The Big Form Factor Guide - BTX
BTX, Balanced Technology eXtended, is a standard developed by Intel primarily to improve processor cooling compared to ATX. It provides a more direct path for air from the front of the case, across the processor, and out the back of the case. BTX attempted to preserve compatibility with ATX as much as possible, so ATX power supplies work (provided their cables reach), and expansion cards compatible with an ATX system are also compatible with a BTX system.
BTX differs from ATX primarily in the case, motherboard, and processor heatsink. The motherboard is considerably rearranged, and mounted on the opposite wall of the case. The processor heatsink is shorter and more squat. Air is meant to flow through essentially the center of the case in a straight line, rather than snaking a path from the front-bottom to the top-back as in a typical ATX system.
The variants of BTX all share the same motherboard "depth" of 266.70 mm, and the same power connections etc. They differ only in width (and therefore in available expansion slots).
BTX
The primary version, with a motherboard length of 325.12 mm and a maximum of 7 add-in card slots. Regular BTX motherboards and chassis must support all 10 of the motherboard mounting holes in the BTX spec.
BTX uses the same power supply connectors as ATX v2.0. This means both a 24-pin primary connector and a 4-pin +12 V connector on the motherboard. As with ATX v2.0 motherboards that use this standard, older 20-pin power supplies will still usually work. Supplies without the 4-pin +12 V connector may not be able to run the system stably.
| Maximum slots: | 7 |
| Width: | 325.12 mm (12.8 in) |
| Depth: | 266.7 mm (10.5 in) |
| Mounting holes: | 10 |
| Introduced: | 2003 |
| Link: | BTX standard |
microBTX
A somewhat smaller version of BTX, targeted at smallish OEM computers (Dell, Compaq, Gateway) that are highly cost-sensitive.
| Maximum slots: | 4 |
| Width: | 264.16 mm (10.4 in) |
| Depth: | 266.7 mm (10.5 in) |
| Mounting holes: | 7 |
| Introduced: | 2003 |
| Link: | BTX standard |
nanoBTX
Introduced after the other standards, nanoBTX is intended to bridge the gap between microBTX and picoBTX. It essentially increases the size of picoBTX just enough to add one more expansion slot, but is otherwise very close to picoBTX. It even uses the same mounting holes.
| Maximum slots: | 2 |
| Width: | 223.52 mm (8.8 in) |
| Depth: | 266.7 mm (10.5 in) |
| Mounting holes: | 4 |
| Introduced: | 2005 |
| Link: | BTX standard |
picoBTX
A very small variant intended for Small Form Factor systems.
| Maximum slots: | 1 |
| Width: | 203.20 mm (8 in) |
| Depth: | 266.7 mm (10.5 in) |
| Mounting holes: | 4 |
| Introduced: | 2003 |
| Link: | BTX standard |