This is the VOA Special English Economics Report.

Once, stocks were traded through the open outcry system, with men shouting share prices on the floors of stock exchanges.

But the sights and sounds of stock traders furiously exchanging securities has mostly disappeared. They have been replaced by fast, interconnected computers.

Joe Saluzzi is a head of equity trading at Themis Trading in New Jersey.

JOE SALUZZI: "The equity market has changed. It's no longer what you see on TV, it's no longer guys with colored jackets running around the floor anymore. That's the show, that's the TV studio. The equity market is a bunch of co-located computers strung together by a bunch of wires, everyone trying to race to zero. The speed of light is the goal—the speed of light! That's what we're looking at now."

Computers can process stock trades in thousandths of a second. Andrew Haines of Gain Capital is an online broker.

ANDREW HAINES: "A millisecond can mean millions of dollars to the success of your strategy. Having a one, two, three-millisecond advantage over other traders may mean that you get into a trade at a preferable price."

Andrew Haines says an estimated 70 percent of all stock trades are high-frequency trades made with computers. Stocks may be held for only seconds. But fast trades are also blamed for big moves in stock prices.

On May 6th 2010, the leading measure of American stocks briefly fell nearly 1,000 points, or about nine percent. The Dow Jones Industrial Average then recovered much of those losses by the end of trading that day.

The Securities and Exchange Commission ordered steps to prevent future "flash crashes" like that one. Joel Hasbrouck of New York University says those steps are working.

JOEL HASBROUCK: "They're called circuit-breakers, and basically what they mean is that when a stock has moved by a large amount in a short period of time, there's a trading halt."

Joe Saluzzi of Themis Trading says the main problem with high-speed trading is an unbalanced market.

JOE SALUZZI: "The stock market used to be a predictor of the future economy. Now I think the stock market is a backwards predictor. It doesn't tell you, it's not forecasting. It's forecasting the next microsecond move."

But Joel Hasbrouck says high-speed trading can, in fact, reduce sharp rises or drops in stock prices.

JOEL HASBROUCK: "In normal circumstances, high-frequency traders act as market-makers. That means, they stand by passively waiting to buy or sell from whoever comes into the market needing to trade. In that capacity, they actually help stabilize the market."

High-frequency traders use computers to follow stock price movements, buy shares and then sell them to another buyer, all within seconds. This is the opposite of long-term investing. American and European officials are considering ways to limit high-frequency trading. They say this may help protect against extreme market volatility in the future.

And that's the VOA Special English Economics Report. I'm Mario Ritter.

outcry: a loud utterance; often in protest or opposition 强烈抗议；大声疾呼；尖叫；倒彩

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（来源：VOA 编辑：Rosy）