The Battle for the Matching Engine

In Chapter 27, Larry Harris looks at the ultimate showdown: The Floor vs. The Computer. In an age of high-speed fiber optics, why do we still have people in colorful jackets yelling at each other in lower Manhattan?

The Case for the Machines (Automated Systems)

Most modern trading is automated. Whether it’s an ECN like Island or a wholesaler like Madoff, computers are great at:

• Operational Fairness: A computer doesn’t have “friends.” It follows the rules (Price-Time Precedence) exactly as programmed.
• Audit Trails: Every single click and trade is recorded perfectly. It’s much harder to cheat when there’s a flawless digital log.
• Scalability: A computer can handle 10 million orders a second. An oral auction in a “pit” breaks down if more than a few hundred people are yelling at once.
• Distributed Access: You can trade from your couch in pajamas. You don’t have to be a 6'4" guy with a loud voice to get a fill.

The Case for the Humans (Floor-Based Systems)

If computers are so much better, why hasn’t the NYSE floor closed? Because humans are better at negotiating complex info.

• The Identity Audit: When a massive block order arrives, floor brokers look each other in the eye. They ask: “Is this the full size?” “Is your client smart money or just a pension fund?”
• Selective Exposure: Humans can reveal a little bit of an order to test the water. Computers usually require a “firm” commitment, which can be dangerous for a whale.
• Trust: In the “Upstairs Market,” relationships matter. If you lie to a floor broker, you’re dead in that pit. That social pressure keeps the market moving during times of stress.

The Problem of “Fast Markets”

In an oral auction, when things get crazy, the market is designated as “Fast.” This is basically an admission that the humans can no longer keep track of the best price. In an automated system, there is no such thing as a “fast market”—the computer just keeps matching until it runs out of orders or the power goes out.

Reliability: The Machine’s Achilles Heel

Harris gives a scary example: Imagine you’re an arbitrageur and you’ve bought half of your hedge on an electronic exchange. Suddenly, your internet goes out. You are now “naked” in a volatile market and you can’t even see the price to get out. Floor traders have a physical presence. As long as the building is standing, they can trade.

Summary: The Hybrid Future

We are moving toward a world where small, “easy” orders are handled by machines (immediacy), while large, “difficult” orders are handled by humans (depth).

The only reason some inefficient floors still exist is the Order Flow Externality we talked about in Chapter 26. People trade there because everyone else trades there. But as tech gets better at simulating human trust and selective exposure, the jackets are slowly fading away.

Next time, we’ll look at the scariest part of the market: Bubbles, Crashes, and Circuit Breakers.

Next Post: Bubbles, Crashes, and Circuit Breakers