at and atx psu's

I was just wondering if an at power supply is smaller than a atx power supply??

any help is would be great

 

AT PSUs are much bigger. Different shape too.

 

alright thanks

 

While there may be a physical difference, the key differences are this:

AT have a wired switch that goes to the front of the case; ATX work in conjunction with the motherboard for a soft switch. Here, there is still a switch up front, but it's wired to a header on the motherboard.

The other major difference is the main power connetor.
AT power supplies use 2x 6-pin leads, where ATX uses one 20 or 24-pin (24-pin is newer).