How Computers Changed Wall Street
Interest in the new stock market began with the case of Sergey Aleynikov, a Goldman Sachs programmer accused of taking trading code. The case exposed a strange contradiction. If the code was so powerful that it could threaten markets, then the deeper question was why such code was normal inside a major bank. That question opened the door to a world most people never see: high-frequency trading, where computers react to market information faster than any human can think.
The shift toward this world accelerated after the stock market crash of 1987. During that panic, many human brokers simply stopped answering their phones rather than take more sell orders. Regulators and exchanges responded by pushing markets toward automation, believing machines would be more reliable than people under stress. Over time, the old image of traders shouting on exchange floors gave way to silent servers sitting in heavily guarded data centers.
By the 2000s, the stock market no longer operated as one visible place. It had become a scattered network of exchanges, dark pools, private routing systems, and cables running between New Jersey, Chicago, and New York. Orders no longer moved through a simple public market. They passed through a hidden electronic system that even many professionals did not fully understand.
Brad Katsuyama arrived on Wall Street from Canada believing the market mostly did what it claimed to do. At the Royal Bank of Canada, he built a successful career and trusted the screens in front of him. Then he noticed a pattern that made no sense. Whenever he tried to buy stock, shares that seemed available would disappear the moment he pressed Enter, and the price would move against him before his order was finished.
That experience changed everything. It suggested the market was not merely reporting supply and demand but reacting to his own attempt to trade. He was not just observing the market. His behavior was being detected, interpreted, and used against him in real time.
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