What are some characteristics that define a ATX motherboard?

Answer 1

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.

Answer 2

ATX is a "form factor", or standard size, of motherboard used in mid-tower and full-tower PCs. ATX measures approximately 305 mm × 244 mm (12" x 9.6"). Advance Technology eXtended. It is the standard that followed baby AT and defines physical size and standardizes socket pinouts of motherboards.

Answer 3

(Advanced Technology EXtended motherboard) The PC motherboard that superseded the Baby AT design. The ATX layout rotated the CPU and memory 90 degrees, allowing full-length expansions to be plugged into all sockets. The power supply blows air over the CPU rather than pulling air through the chassis. Introduced in 1995, the ATX was the first PC motherboard to not only include I/O support (serial, parallel, mouse, etc.), but to place all the connectors directly on the motherboard. Prior to the ATX, only the keyboard connector was attached to the motherboard. Numerous variations of the ATX were subsequently introduced with both smaller and larger form factors, including the microATX, Mini ATX, FlexATX and Extended ATX

Answer 4

There are many ATX motherboard types, uATX, MATX, Baby-ATX etc. The standard has also been modified as the power requirements have changed.

Generally, they are:

Some version of the ATX power supply connector (currently 24 pins plus the auxilary 4-pin 12volt connector;

The locations of the holes to screw it into the case;

The location of the ports cluster, to match the cut-out in cases for it; and

The location of the expansion slots.

formfactors.org can tell you more.