The new 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* in mind. In addition to smaller than microATX system sizes, BTX also was designed to scale up to tower size systems using the same core layout by increasing the number of system slots included. You can get more information about BTX over here or you can download the developers specifications over here.