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).