Not sure about the various models other than the C has 2 external USB's and the E has 6 I think. The ASUS site should have more info. I bought a refurb'd "C" and so far am very happy with the board. It has a snappy feel to it that my Abit KX7-333 did not have. It was buggy so I pulled it. May RMA it later or just skip and wait for a worthwhile upgrade. This is the second A7V266-C that I built and they have been excellent, at least the first one. This one is still buring in, but so far it has been holding up without a problem.