What is the differences between server and domain name?

Question

An URL is in the format of:

scheme://server:port/pathname      

What is the differences between server and domain name here? //superuser.com/questions/ask is a (relative) URL.

The scheme is omitted (http:). The server is superuser.com. Maybe the server is equal to the domain name?

Solution

A server is a physical piece of hardware. This hardware has multiple IP addressess associated with it. A server is often referenced by referring to one of the IP addresses associated with it, or by the domain name which points to that IP address.

It is worth noting that a server can (and in the case of web sites, usually does) have multiple domains associated with it.

Technically speaking I would argue that it is incorrect to use "server:port" in an HTTP url - it should be domain:port, but it is common practice to do so anyway. In some addressing schemes (like FTP for example) calling it a server makes sense because there is no difference if the server is referred to by (any) domain associated with it or its IP address. [ HTTP has additional logic so the server can determine which domain is being referred to ]

Comments

[HikeMike]

People used to type go to e.g. http://www.example.com instead of http://example.com. That's because in the domain example.com (of e.g. an organization), the host known by convention as www served the web sites of that organization.

[HikeMike]

"Server here means server IP" is nonsense. Also, Google has a lot of IP addresses, 74.125.224.72 is not universal.

[JdeBP]

Perhaps you should expand upon the 'L' of "URL" meaning "locator". The server is identified and located by the host and port in the authority component.

[davidgo]

Sorry, but this is wrong. the "//" means "Start of a network path reference", and is not shorthand for anything. [ See Section 4.2 of RFC3986 ]. The leaving out of the http/https part means that this should be derived from already known information - ie this part is relative. Also, http or https are only 2 schemes of a very large number of well over 100 accepted schemese - see en.wikipedia.org/wiki/…

[Sparky_47]

I'm not talking about the // per se. Shorthand refers to the fact that you can omit the http(s): part of a URL, in HTML5. What I said should be read in the context of how the question was asked.