From Parallel Ports to Thunderbolt: How Mobile Interfaces Evolved

Parallel vs Serial Ports

Early computers used parallel ports, transmitting 8 bits simultaneously over 8 wires, offering high speed but limited to short distances due to interference and higher cost. Serial ports send the same 8 bits over a single wire; although slower, they are more stable, cheaper, and became the mainstream choice. Modern USB adopts serial communication.

USB Type‑A and Type‑C

Today’s primary data interfaces are USB Type‑A and Type‑C. Type‑A was popular a few years ago but is gradually being replaced by the smaller, reversible Type‑C, which has more pins, higher bandwidth, and supports both data and power transmission.

Type‑C’s additional pins enable greater bandwidth and scalability, and it fixes the “one‑way insertion” limitation of Type‑A.

Thunderbolt

Thunderbolt, co‑developed by Intel and Apple, is now common on high‑end PCs. Since Thunderbolt 3 it uses the Type‑C connector with up to 40 Gbit/s speed. The Thunderbolt 3 controller can integrate a USB 3.1 Gen 2 controller, allowing USB devices, and supports DisplayPort video transmission.

Thunderbolt 4 does not increase raw bandwidth over Thunderbolt 3 but introduces dynamic bandwidth allocation, raising non‑video data capacity from 22 Gbit/s to 32 Gbit/s, while still reserving 18 Gbit/s for video.

Images above illustrate the discussed interfaces.