BRAD BAILEY was visiting the trading floor of an investment bank in New York City when he first noticed it. As a former Wall Street trader, he should have felt at home amid all the screens, phones and bustle of billions of dollars in trades. But that was just it: there wasn't any bustle. In fact, there were hardly any traders. "You could hear a pin drop," he recalls. Then it sank in: machines had taken over the role of people and computer servers don't make any noise.

There's a quiet revolution happening all over the financial world. Gone are the days of Gordon Gekko lookalikes screaming obscenities and dumping a loss-making stock onto an unsuspecting market. Investors have realised that the processing speed and sheer volume of trades a computer can make can help them to outwit the sharpest of dealers. As a result, they are investing heavily in ...