You will want a switch, especially if it's likely that more than one MD will be used simultaniously.
A hub basicly has 100MB available for all the ports, and sends all the info to all the ports, meaning that at full 'troughput' a hub can only serve each MD with 15-20MB at best (not counting all the 'collisions'), far too little for a stable and good system.
A switch will route the data to the appropriate receiver, threreby speeding up delivery considerably.
(this is the quick and dirty simplified explenation, for more info I suggest you try wikipedia.com
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