When registering a web address, you have many options for choosing the right domain extension. Domain providers offer over 1500 top-level domains (TLDs) for various purposes today. If you wish, they can represent a country or language, be intended for organizations and institutions, or indicate the theme of your website. One popular TLD for some time now is the .io domain, whose original meaning related to a country has little to do with its success. What does .io mean? Why is this domain extension so popular in the world of computer science and tech companies?

What is a top-level domain (TLD)?

Each address resolved by the Domain Name System (DNS) of the World Wide Web consists of several elements. These components always follow a hierarchical structure. The highest and most visible hierarchical level is the top-level domain or TLD. As this element is always at the far right of the address, it is also known as the “domain extension.” In the address http://www.example.org, the org part would be the top-level domain.

The allocation of the more than 1500 TLDs is regulated by ICANN (Internet Corporation for Assigned Names and Numbers), a department of the nonprofit organization IANA. Two different types of domain extensions can be distinguished: on the one hand, there are generic top-level domains (gTLDs), such as .beauty or .blog, which present a theme. On the other hand, there are country code top-level domains (ccTLDs), such as .es or .io, which this article addresses.

What is a .io domain?

The .io domain extension is a ccTLD, meaning it is a geographic top-level domain, assigned to the British Indian Ocean Territory in 1997. The domain is managed by the UK-based domain registrar Computer Bureau (ICB), which since 2017 has been a subsidiary of the American group Afilias, who also administer TLDs .info, .mobi, and .pro, among others.

From the beginning, the .io domain has not been used to refer to this territory, which is normal considering that there are no permanent legal residents in the British Indian Ocean Territory. Any individual or legal entity can register a .io address, regardless of their residence or location (the address can consist of 2 to 63 alphanumeric characters). Only addresses with added second-level domains, such as .com, .net, or .gov, would be blocked. Therefore, a domain like mybusiness.net.io could not be registered.

What does .io mean?

Originally, the .io domain meant the Indian Ocean. However, nobody associates the domain with this British overseas territory, whose last vestige is the Chagos Archipelago (a group of islands spanning 63.17 km²). Probably, almost none of those wondering what the .io domain means would imagine that the TLD is a geographical reference.

Therefore, the question should not be what the .io domain means, but what meaning is attributed to it. Here are two possible functions:

  • Input/Output (I/O or IO): In computer science, the abbreviation I/O or IO stands for Input/Output, which is the foundation of communication between computer systems and the external world. Similar to the generic TLD (Top-Level Domain) .app, which is the ideal extension for mobile app developers, the .io domain is appealing to tech companies due to this meaning.
  • Domain hack: The top-level domain .io is also significant as an extension for domain hacks. With some creativity, one can invent web addresses like rad.io, portfol.io, by combining a name with the appropriate domain. A popular example is the domain rub.io, which American politician Marco Rubio used in his 2016 presidential election campaign.

Fun fact: Fashion company Levi Strauss & Co. registered its first web address under the ccTLD (Country Code Top-Level Domain) .io in 1998.

Why is the .io domain so popular in the field of computer science and tech startups?

According to w3techs.com figures, as of 2021, about 0.5% of websites are registered under the TLD .io. This places the extension on par with geographic domains like .it or .pl, for example.

The high popularity is largely due to the meaning of the letter combination IO: users such as developers or computer enthusiasts have an initial clue about the theme of a website’s content by seeing the Input/Output abbreviation in the domain. On the other hand, this domain extension also represents an easily readable and pronounceable alternative to classic high-demand top-level domains, making it a good option if the .com extension or similar ones are unavailable.

Advantages and disadvantages of the .io domain

The .io domain has gained significant importance in recent years. This geographic domain extension has been well-received in the tech environment, as well as by users or companies unrelated to computer science but interested in creating clever addresses. To conclude, we compare the most important advantages and disadvantages of a domain under the TLD .io:

Advantages of .io DomainDisadvantages of .io Domain
Quick recognitionLess accessible for non-technical users
Many domains are availableMay give the impression of a small project
Ideal for domain hacksRelatively expensive
Google treats .io as a generic TLDRevenue does not benefit local residents, unlike other ccTLDs
Shorter than alternatives like .com or .app