Question

Anybody knows where the “://” or the “//” comes from in most URIs syntaxes?
For instance, why isn’t it written like “http:www.example.com“?

Answer 1

a1kmm’s answer is good for specific application to URLs, but if you’re curious as to the semantic origin of the double slash, take a look at this article:

http://www.w3.org/DesignIssues/Axioms.html

It is worth noting that the syntax
with the double slash can in fact be
extended for use with a triple slash
if one wanted to be able to start at
any level in a much more complicated
hierarchical structure. For example,
suppose international telephone
numbers were to be extended to cover a
planetary code in the future. Then the
planetary code could be attached to
the front of the international code.
The triple slash could introduce the
interplanetary code, and the double
slash would introduce the
international code. Indeed, this is
how the double slash came to be: when
hierarchical naming schemes such as
those in unix file systems was
extended to a networks file system on
the Apollo domain the extra slash was
introduced. Similarly, Microsoft NT
networking now uses double backslash
in exactly the same way.