Either option is useful, both options are still currently used and practical in the industry. I've worked at different companies where the philosophy is totally opposite. It all depends on the component selection, from the power supply , everything in between, size of the circuit card, to the backplane. There are non-standard systems which are migrating to the central power supply design (and using standard backplanes or edge connectors), but there is usually a small DC-DC converter onboard dedicated for low voltages. Then with newer components(ex: new static rams) , they draw less power, circuit cards with power/ground layers have more power and thermal capacity(power density) . I recall the S-100 cards I used back then were at most only 2 layers, so the power and thermal characteristics were limited as compared to say the VME cards. I think the S-100 breadboards that are still available are only 2 layers. In the local power supply option, we had DC-DC converters which have such a low footprint where we embedded this on the circuit card(24"x24") and the power supplies (via backplane) would have power rails supply 48V to every card. In a central power systems, we had circuit cards just as large and all the power supplies just sit at the bottom of the 19" rack and supply the backplane with various voltages, with thick, huge cables. The backplane is important such that you don't want to experience too much impedance or resistance (thicker copper is better), solid power and ground layers is expected. You might want to use an off-the-shelf backplane for this purpose--there might be limited availability of S-100 backplanes with these features.The commodity backplanes in use today still have a central power supply, such as CPCI, with many layers. The most they would have onboard is another little DC-DC converter for low voltage components(3.3v or 2.5v). With the traditional S-100 backplane and a central power supply you might experience less power capacity. But this can be compensated by using newer components to reduce the power consumption. You can build either type of system so long as you determine the maximum power capacity per slot.. =Dan [ My Corner of Cyberspace http://ragooman.home.comcast.net/ ] Warren Wolfe wrote: