http://online.wsj.com/article/SB116615315551251136.html?mod=hps_us_pageone NORTH KANSAS CITY, Mo. -- About four years ago, Dave Cummings moved his trading firm's computers from a storefront in this Kansas City suburb to buildings in New York and New Jersey that house central computers for two big electronic stock exchanges. The move shaved a precious fraction of a second from the time it takes Mr. Cummings's firm, Tradebot Systems Inc., to buy or sell a stock on computer-based exchanges like Archipelago. It now takes Tradebot about 1/1000 of a second to trade a stock, compared with 20/1000 before the move -- a difference of about the time it takes a computer signal to zip at nearly the speed of light from Kansas City to New York and back. That may not seem like a big difference, but in Mr. Cummings's obscure corner of the stock-trading universe, speed is critical and fractions of seconds loom large. Tradebot's computers are programmed to detect, among other things, tiny, fleeting differences between bid and offer prices of stocks, then to pounce, buying stocks at one price and almost immediately reselling them for a fraction more. If his firm hadn't moved its computers, says Mr. Cummings, "we'd be out of business." [D C] Dozens of other firms, ranging from Citadel Derivatives Group to a brokerage unit of J.P. Morgan Chase & Co., also employ split-second trading strategies. That has set off an arms race to shave the time it takes for orders to reach the computers of electronic exchanges. In their quest for the choicest locations, at least 40 of Tradebot's competitors have carted their computers to the same buildings, a practice known as co-location. The kind of trading practiced by Mr. Cummings is a particularly fast form of "algorithmic" or "black-box" trading, in which computer programs decide when to buy and sell securities. Hedge funds such as SAC Capital Advisors, D.E. Shaw & Co. and Renaissance Technologies have been using computers in their investment strategies for years. These days, a variety of new computer strategies rely on lightning-quick trading. For example, computers are being programmed to take news headlines into account when executing trades, and media companies including Dow Jones & Co., publisher of The Wall Street Journal, and Reuters Group have begun releasing news in computer-readable formats that cater to them. Mr. Cummings's strategy -- which is shorter term than most and is highly reliant on speed -- was made possible by the growth of electronic-trading networks. These trading platforms -- Globex at the Chicago Mercantile Exchange, Archipelago at NYSE Group, INET at Nasdaq Stock Market and others -- account for more than half of all trading in household-name stocks and financial futures contracts. Trading mostly Mr. Cummings's own money, privately held Tradebot, which has about 20 employees, makes between $30,000 and $150,000 a day and up to $20 million a year, people familiar with its finances say. Electronic exchanges use computer systems to match buyers and sellers. They execute orders without involving floor traders known as specialists, who arrange transactions through auctions on the NYSE. For years, these specialists and the Wall Street dealers who traded Nasdaq stocks profited on gaps between bid and offer prices.