10/100 Half Duplex means it can send OR recieve at 10/100mbps but not both ways simultaneously. You have to finish sending at 10/100 to recieve at 10/100. You cannot send at recieve data simultaneously at those speeds. Full Duplex means it can send AND recieve at 10/100 simultaneously both ways. I guess those networking reviews I wrote a while back helped me =). Merry Christmas!