The Difference Between 686A and 686B
There is not much to be said about the Southbridge VT82C686B. The circuit diagram is nearly identical with VT82C686A except for the added UltraATA/100 function.
The pins of the 686B-chipset are fully compatible with 686A. Theoretically, boards designed for 686A could be equipped with 686B as well. Most of the manufacturers do that and change the name of the board in order to display the new UltraATA/100 feature. AOpen, Luckystar or MSI call it "Pro" and Soltek adds an "X" to the original name. Only Biostar seems to think that it is not necessary to show the difference between the three different M7VKB boards to the customers. You can get this product with UltraATA/66 as well as UltraATA100.