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A Uniform Resource Locator, or URL, is a specific type of web address. It serves as a reference to a resource on the World Wide Web. A URL identifies the exact location of a resource on a computer network. It also provides a mechanism for retrieving that specific resource. While many people use the term Uniform Resource Identifier (URI) interchangeably, a URL is actually a specific type of URI. URLs are essential because they allow different computers to find and share information.

To understand how a URL works, you must look at its syntax. Every HTTP URL follows the syntax of a generic URI. A web browser uses the URL to perform a request to a specific host. By default, this request happens on port number 80. If the URL uses the HTTPS scheme, the connection is secure. This means the requests and responses happen over a protected connection. The browser reads the address to know exactly where to go and how to talk to the server.

A URL is composed of several distinct parts that work together. For example, consider the address https://www.example.com/index.html. The first part, https, is the protocol. The protocol tells the computer which rules to use for the connection. The next part, www.example.com, is the hostname. This identifies the specific server on the network. Finally, index.html is the file name. Slashes are used to separate the directory and the filenames.

Different applications use different protocols within a URL. While HTTP and HTTPS are most common for web pages, other types exist. For instance, FTP is used for file transfers. The mailto protocol is used for email. You might also see JDBC used for database access. This variety allows the URL system to point to many different kinds of digital resources.

The history of the URL involves important collaboration. Tim Berners-Lee, the inventor of the World Wide Web, helped define the URL in 1994. He worked with the URI working group of the Internet Engineering Task Force (IETF). This collaboration began with a session in 1992. Early drafts even called these "Universal Document Identifiers." The name was changed to "Uniform" between June and October 1994. Berners-Lee later expressed regret regarding the syntax. He wished he had used slashes instead of dots to separate domain names.

As the internet grew, the system had to support more people. Internationalized Resource Identifiers, or IRIs, were created to help. An IRI is a form of URL that includes Unicode characters. This allows users to use their own local alphabets and writing systems. The domain name in an IRI is called an Internationalized Domain Name (IDN). Software automatically converts these into punycode so the Domain Name System can use them. For example, a Chinese URL is converted into a format starting with xn--.

Path names in a URL can also be specified in local writing systems. If the characters are not part of the basic set, they undergo percent-encoding. This converts characters into hexadecimal format. For example, a Japanese URL becomes a long string of percent signs and numbers. The target computer then decodes this address to display the correct page. This process ensures that anyone, regardless of their language, can navigate the web.

URLs also include special types like protocol-relative URLs. These are also known as protocol-relative links or PRURLs. These links do not specify a protocol at the start. Instead, a link like //example.com will simply use the protocol of the current page. This is usually either HTTP or HTTPS. This flexibility helps web developers manage links more easily across different types of secure or non-secure connections.

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