There are many places where one could purchase an ATX motherboard. Stores like BestBuy and Conrad have them in stock. Alternatively one could buy them at Amazon.
ATX Ver 1.0 has one 20 pin port ATX Ver 1.1 has one 20 pin port and a 4 pin port ATX Ver 2.0 has one 24 pin port and a 4 pin port
ATX
The ATX form factor is an ancient one. Modules can range all the way from 72-pin DIMMS to DDR3.
There are many motherboard sizes, and ATX is simply one of them. Others inlude Mini-ITX, MicroATX, etc.
20 pin P1 connector.
Someone can purchase a AM2 motherboard from a number of companies such as Amazon. Amazon has a large selection of AM2 motherboards from various manufacturers.
All motherboards will work fine, save server one. Consider getting a standard ATX or micro-ATX motherboard.
The atx 12 connector is one of the motherboard power connectors and used for 12 volt power connect for cpu voltage regulator.
There are many differences between AT and ATX motherboards. The most noticable, without disassembly, are probably the keyboard connector (AT is much larger) and the power switch. The power switch for an AT motherboard clicks on and clicks off. The power for an ATX motherboard is a momentary push button that is always open unless pressed. Internally the best indicator is the power supply connector to the motherboard. An AT motherboard uses a two piece single row connector. An ATX motherboard connector is one piece with two rows of ten connections.
One can purchase a Foxconn motherboard online at a variety of different websites. One can purchase a Foxconn motherboard at websites such as Amazon and eBay.
One of the best is the Intel D865GVHZ ATX Motherboard w/Pentium 4 2.4GHz CPU.
It depends on the type of board you have. Obviously a laptop mobo (motherboard) is going to be smaller than one in a desktop. And again a desktop one is going to be different than one for a server. Motherboards are categorised by a thing called form factor. So for example the form factor of an ATX board is going to be different than the form factor of an extended ATX. ATX would be the standard board you would use in a desktop PC. Whereas you might use mini-ATX for one of those new mini computers you see, or you might use extended-ATX in a server. So when someone asks what form factor the board is, they're really just asking "is it atx or micro-atx or mini-atx etc..." And obviously each form factor is going to be different in size. There are some very good online tutorials about mobo's, check google.