In the time it takes you to blink (300ms), an HFT algorithm has traded 10,000 times. The constraint is no longer human reaction time. The constraint is Physics.
Light travels 30% slower in glass fiber than in air. Chicago to New Jersey is ~1,200km. On fiber, that round-trip is ~6ms. On microwave towers along the straight-line path, it's ~4ms. That 2ms delta is the difference between being first in queue and getting the trade your competitor rejected — adverse selection in action.
The OS adds another layer of friction. The Linux kernel introduces ~20µs of scheduling overhead per syscall. Kernel bypass (DPDK, Solarflare) eliminates this by writing directly to the NIC, bypassing the kernel network stack entirely.
This article covers the full stack: microwave topology, kernel bypass networking, FPGA order entry, colocation power constraints, and the serialization tax (Protobuf vs Simple Binary Encoding).