Same as a washing machine, best if you cold and hot feed as it will not need to heat the water but will work with only a cold feed, just takes longer and slighty more costly to run.
Most of them only have a cold water feed. Reason being that they use only a small amount of water, and because the water in the pipes is cold, it would take too long for the hot to arrive at the machine. All that would happen is the pipes would fill with hot!
I recommend cold fill. All manufacturers books contradict each other but I read in one about 20 years ago that cold should only be used because if you have protein food stuffs on plates - such as egg - hot water will bake it on more on contact - therfore the cold water has chance to loosen it first and then wash it off completely as the water warms up. However, dishwasher detergents do claim they can remove anything these days but I don't think they are as good as they were 20 years ago when you could smell the good old bleach in them giving you the knowledge that your crockery was sanitised. I think now they can't do this as many a design on a plate has been washed off !