Port and Starboard: Maritime Terms That Reshaped Navigation and Computing

Wherever you board a plane today, the door is always on the left. New York, Tokyo, Dubai — it makes no difference. At thousands of airports across the world, passengers step through the left-side door of the aircraft. This is not a matter of design convenience or coincidence. The reason traces back to a single steering oar that Nordic sailors fixed to the right side of their ships thousands of years ago. And there is a far more surprising connection: the “port” that your computer uses to send and receive data across the internet is rooted in the very same word.

A Seafaring World Without Left-Handedness

Ancient vessels had no rudder as we know it today. Sailors drove a large wooden oar into the water from the right rear of the hull and pushed or pulled it to steer. This was the steering oar — the steerboard.^[1]

Why the right side? Because most sailors were right-handed, and controlling the oar with the right hand was far more natural. In Old Germanic, the word for this side was steorbord, which Old English also adopted. Here, steor means “to steer” and bord means “the side of a ship.”^[2] Over time, steorbord became starboard.

Placing the steering oar on the right created a practical problem when docking. If the hull was brought up flush against a quay, the oar would be crushed against the dock wall. So sailors always docked with the left side against the pier. The ship’s left side had long served as the loading side, and in Old English it was called bæcbord — literally “the side behind the helmsman’s back.”^[2]

In Middle English, bæcbord shifted to laddeborde and then to larboard. Etymologists believe this evolution was linked to the verb meaning “to lade” (to load cargo). Larboard was, in plain terms, “the side of the ship where cargo is loaded.”^[2] Language reflected function.

Confusion Breeds a New Name: From Larboard to Port

The trouble was that larboard and starboard sounded dangerously alike. On a storm-swept deck, shouted across the length of a ship, the two words were nearly indistinguishable. A mishearing could send a vessel lurching the wrong way. Many groundings and collisions in the era of sail were likely born from exactly this confusion.

From the early nineteenth century onward, a growing practice took hold in the British Royal Navy: using port in place of larboard. “Port” was already the word for harbour, and its logic was geographic — the left side was the side that faced port when docking.^[3] Crucially, the word opened with a completely different consonant from starboard, making confusion far less likely in noisy conditions at sea.

On 22 November 1844, the British Admiralty issued an official circular formally abolishing the word larboard and establishing port as the standard term. The circular stated the reasoning plainly: “The distinction between starboard and port is much more marked than between starboard and larboard.”^[3] The United States Navy followed suit two years later, in 1846.^[3]

The impact of this decision went far beyond a simple word swap. A term that sailors the world over had used for centuries was erased, and a single unified standard took its place. In an era when international communication was becoming the norm, this was a decisive act of standardisation for maritime safety.

Navigation Lights: Direction Becomes Colour

The distinction between port and starboard did not remain confined to speech and text. At night or in fog, ships needed a visual language to communicate their position and heading to one another. The answer was navigation lights.

Britain’s 1846 Steam Navigation Act made it compulsory for all British vessels to carry a red light on the port (left) side and a green light on the starboard (right) side.^[4] The colour logic is intuitive. Because red universally signals danger, an approaching vessel that sees the other ship’s red port light understands: “I am looking at their left side — we are on a collision course.” Green means “I am looking at their right side — they are moving away from me.”^[4]

At the world’s first international maritime conference, held in Washington, D.C. in 1889, twenty-seven nations adopted this red-and-green system.^[4] Entering into force in 1897 as an international standard, the system remains in use today. The International Regulations for Preventing Collisions at Sea (COLREGs), adopted internationally in 1972 and in force from 1977, enshrine this colour code in current law.^[5]

Maritime Language Takes Flight

When aircraft arrived at the dawn of the twentieth century, aviation simply inherited seafaring convention wholesale. Aircraft carry a red light on the port (left) wing and a green light on the starboard (right) wing. Pilots call left “port” and right “starboard.” The captain sits in the left seat.^[6] All of these practices were transplanted directly from maritime tradition.

The most familiar example of this inheritance is the boarding convention. Why do passengers always board from the left — the port side — of the aircraft? The answer lies not in functional necessity but in historical custom. Modern aircraft are not designed with a structural left-right asymmetry. There are doors on the right side too, and loading cargo from the left is technically possible. If every airline in the world swapped the roles of port and starboard overnight, the aircraft themselves would function without issue. The problem is that thousands of airports’ jet bridges, fuel vehicle routes, and ground handling systems have been standardised around the current convention over decades.^[6]

In the early days of commercial aviation, it was natural to follow maritime practice directly. Placing service vehicles and cargo equipment on the right (starboard) while assigning passenger boarding to the left (port) allowed both operations to proceed simultaneously on the ground. That practical separation hardened into convention, airports were built around it, and today’s standard was born. The fact that airports worldwide are designed with left-side jet bridges is the memory of an ancient steering oar, carried across millennia and cast in concrete.

Port Enters the Computer

The story does not end there. In the latter half of the twentieth century, the word “port” crossed into an entirely new domain: computers.

In fact, “port” appeared in computing first as a physical connector — before network ports came to prominence. Personal computers of the 1980s were fitted with serial ports and parallel ports. Serial ports sent data one bit at a time in sequence and were used to connect modems and mice. Parallel ports transmitted multiple bits simultaneously and were used primarily with printers. These physical openings were called “ports” for the same reason as a harbour: they were the gateway connecting the computer’s interior to the outside world.^[7]

Today’s USB (Universal Serial Bus) is, as its name suggests, the successor to serial transmission. USB-C ports, HDMI ports, Ethernet ports — all the connectors lining the side of a modern computer are extensions of the same concept. Just as a ship exchanges cargo through a harbour, a computer exchanges data and power through its ports.^[7]

The concept of logical ports — network ports — originated in the late 1960s with ARPANET, the U.S. Department of Defense–funded network. In the early days, the entry points were called “socket numbers” rather than ports.^[8] On 26 March 1972, Vint Cerf and Jon Postel — two of the internet’s chief architects — published RFC 322, which formalised the list of socket numbers then in use and proposed a systematic registration scheme.^[8] Then in 1981, RFC 793, which defined the Transmission Control Protocol (TCP), established “port number” as the standard term.^[9]

When we use the internet today, every data packet is directed not only to the destination computer’s IP address but to a specific port number. When a web browser opens, requests travel to port 80 (HTTP) or port 443 (HTTPS). Email is sent via port 25 or 465. These numbers are logical entry points inside a computer’s operating system that determine which programme handles which data. Just as a cargo ship entering New York Harbour is directed to a particular berth, an internet packet arriving at its destination IP address is routed to a specific application based on its port number.^[7]

Postel referred to himself, only half in jest, as “the czar of socket numbers” during this early cataloguing work.^[8] The title — part joke, part earnest claim — reveals how urgently a coherent addressing system was needed for the network services then proliferating in an ad hoc fashion. The function Postel exercised is today carried out by the Internet Assigned Numbers Authority (IANA), which manages port numbers from 0 to 65,535.^[9]

One Word, Three Worlds

Tracing the journey of the word “port” reveals how consistently this short word has expressed the same underlying logic across radically different contexts.

The ship’s port side is “the side where cargo comes and goes” — the face of the vessel kept clear of the steering mechanism so that cargo can be handled. The harbour (port) is the city’s entry point for ships. A computer network port is the logical gate through which data flows into and out of a specific service. Physical computer ports — USB, HDMI, Ethernet jacks — are likewise called ports because they are “openings that connect the inside to the outside.”

In all three worlds, “port” points to the same core concept: the boundary point that connects inside and outside.^[7] Starboard was born from the steering oar fixed to the right; port was born from the left side that, precisely because it carried no oar, was free to face the harbour. The reason these two words have endured for thousands of years is not mere tradition. It is that they encode not a direction but a function. Unlike “left” and “right,” which change depending on where a person stands or which way they face, port and starboard are names fixed to the object — the ship, the aircraft — regardless of the observer’s orientation.

Port and starboard have survived across millennia because they are absolute reference points. Confuse a direction and a ship strikes a reef; data flows to the wrong programme; boarding gates fall into chaos. In any domain where accuracy is a matter of life and death, human beings always find their way to names that do not move.