Summary: On today's Planet Money, we discuss high-frequency trading, in which people program computers to buy and sell stocks in quick succession under certain, pre-defined circumstances. The idea is to profit from fleeting changes in the price of a stock. High-frequency traders include big banks and tiny little companies. And they're all trying to be even faster than each other. A few years back, all the high-frequency traders were trying to get a one-millisecond edge over everybody else. Today, they're angling for a one-microsecond edge.
