Trading at the speed of light

Once upon a time, stock exchanges were packed with traders running, shouting, and elbowing one another on an open trading floor. Today, virtually all stock trading is done, well, virtually- through massive, globally interlinked computer systems. The rates of these transactions are now limited only by technology and, increasingly, by the speed of light. So a costly arms race has begun for telecommunications and network links that can give traders a competitive edge as small as a few tens of microseconds.