Difference Between AT & ATX Motherboards
Knowing your motherboard type is a must if you maintain, repair or customize your own computer hardware. A little research into the specific features of the motherboard will help ensure you buy only compatible hardware that won't damage the PC. Common motherboard types include the AT form factor motherboard and its next-generation form factor cousin, the ATX.
Advanced Technology and Advanced Technology Extended motherboards are form factor, a term that denotes the type of hardware and power you can connect to your hardware component. Form factor isn't just a term for motherboards -- the term is used universally for any relevant computer component.
Size and Fit
Both AT and ATX motherboards have been produced in various sizes throughout the years, and the form factors fit different computer cases depending on their size. An ATX motherboard is positioned at a 90-degree angle from the positioning of AT motherboards. As a result, you can never use an AT case with an ATX motherboard because it will not fit.
A notable difference between the ATX motherboard and the AT motherboard is the addition of "sleep mode" to the ATX form factor. Sleep mode is a power management mode in which some of the components power down to save power, but parts of the computer remain ready to boot. The sleep mode reduces power drain when the computer is not in use, while still allowing you to quickly revive the computer and pick up from where you left off. In addition, the power supply in the ATX motherboard more easily converts 5 volt current to 3.3 volts when necessary.
Power connectors differ between AT and ATX motherboards. AT motherboards use two 12-pin plugs to power the motherboard, while an ATX motherboard uses one 20-pin plug for the power supply. When using an ATX form factor motherboard, you must use an ATX power supply. You can use the pin number to identify whether you have the correct power supply for your motherboard.
The AT and ATX motherboards have noticeably different exterior connectors. The AT form factor motherboard is limited to one outside connector, a five-pin DIN connector for the keyboard, while the ATX-style motherboard incorporates many other connectors, including connections for network cards, video cards, sound cards and modems.