The speed of light is a magnificent thing. Using light, data can, and often does, travel at the fastest pace allowed by physics. But sending data is not the only job involved in communication. The data also has to be processed and routed. For these jobs, the speed of light is a curse. If it takes you one nanosecond to decide where a bit needs to go, then that bit has already traveled 20-30cm.

In terms of silicon chips and processing, this is a bit like telling a taxi driver to turn left thirty thousand blocks too late. In effect, this means that to make a routing decision, you may have to store the data in a memory register, make the decision, and then extract it again. At the moment, this necessitates storing the information electronically, a painfully slow process. Of course, engineers know this and use clever strategies to minimize the number of times any sort of decision needs to be made.