Bits on a Wire

Layer 1 moves raw bits over a physical medium: voltage on copper, light in fiber, or waves over radio (Wi-Fi). It knows nothing about addresses or messages, only ones and zeros per second.

That "per second" is where units bite. Link speeds are measured in bits per second (Mbps, Gbps), but file sizes in bytes (MB, GB). One byte is 8 bits, so a 1 Gbps link moves 1000 Mbps, which is only 125 megabytes each second.

Mixing the two up is the classic reason downloads seem "8 times slower" than the plan promised.