Some of the changes that will not be as obvious are to be found in the electrical connections. The 24-pin connector is the same as the ATX12V connector that is typically used for workstations, except that it is based on the CFX12V specification. It is different from ATX in that there are four additional connections for 3.3, 5 and 12 Volt, including the ground wire.
Although BTX compliant motherboards are based on the CFX12V standard, they still function perfectly well with normal ATX power supplies - as long as the additional 4-pin power cable is used (which will no longer be included with BTX).