Somehow I feel you missed the point of the thread... I'm not trying to rig up some arduino project. I'm trying to understand the pin compatibility of 386 and 387 processors with each other and with their respective sockets. And Intel and AMD 386s are pin compatible, as AMD made direct fit replacements for the 386. It's not a brand issue but a package issue because these chips came in different packages and mated to different sockets.