Thank you, came here to mention the penny-spread regulation. It's a little known fact about HFT that the reason speed is the primary advantage, is because the e

Thank you, came here to mention the penny-spread regulation. It's a little known fact about HFT that the reason speed is the primary advantage, is because the exchanges don't allow orders at prices which are fractions of a cent, and its first-come first-serve at each price point. The minimum spread permitted on the NYSE was 1/16 of a dollar (6.25 cents) until 2001, when the SEC forced all exchanges to the "decimal system". So now the minimum permitted spread is one penny. If the exchange allowed orders at prices which are fractions of a penny, then algorithmic trading systems would have to compete on price as well speed. But it would also narrow the spreads, which would mean less profit for the "market makers".