how do I tell the difference between AT and ATX?

[astroview]

Stupid question to an old timer, but I got into computers with the PII, so I mostly deal with ATX mobos.

 

[MillionaireNextDoor]

the easiest way to tell is that ATX motherboards usually has its rear output pointed vertically which attached to the board which most AT has it horizontally (AT has ribbons to connect the output to the mobo). some ATs with vertical outputs are out there though but they're still connected to the motherboard with small ribbons. another way to tell is the power connector on the mobo. ATX power supply connectors are different from AT ps connectors. AT usually has two segments of the connectors which ATX usually has one. many other ways to tell but this is the easiest way

 

[GeoffS]

Uaually, an AT mobo has a big DIN keyboard connector mounted on the mobo, and that's it, whereas an ATX board will have the keyboard, mouse, parallel, serial and USB ports mounted on the mobo. Also, an AT mobo will have two blocks for power connectors, in a single line, whereas an ATX mobo will have a single block of two rows (note: some AT mobos accomodate both AT and ATX power connectors [eg. FIC VA-503+]).

An AT PSU has two connectors to the mobo, and one to the case switch. An ATX PSU has a single power connector to the mobo, and the case switch connects to the mobo also.

An AT case will have the case switch connecting directly to the PSU, whereas an ATX case will have a much smaller cable connecting to the mobo.