RealTek 8139 was 10/100. RealTek 8169 was gigabit. The RealTek OS9 drivers for the 8169 seem to work pretty well. Although, in the Umax S900 they will demand an upper slot, which ethernet cards usually do not do. I've seen multiple reports of problems with the 8139 over the years, unless I'm just reading mtm84's complaint repeatedly in different places.