Dual 386 computer existed in the form of the Compaq SystemPro, but it was only supported by Windows NT 3.1. (It was a custom, asymetric design). As you can see in the picture, there were actually processor daughterboards, not just sockets on the mainboard. You can find a nice file-server comparison including 386 SystemPro in InfoWorld (browse to page 55, there's some problem with googles page numeration). I can't think of any other computer using more than one 386 CPU. There were more dual (and more) 486 based servers, but these were mostly custom designs. (If you browse the pictures on1 and 2 on stason, you probably find some dual 486 motherboards). Dual processor workstation motherboards become more popular with the Pentium and the 430NX chipset (motherboards like Tyan S1462 @stason, manual).