Why we sometimes have to use "www" to write a URL, sometimes not?

Answer 1

"www" is only a subdomain. It stands for "World Wide Web". This was initially used to distinguish the Web part of the Internet from the other parts like Archie, Gopher, etc. Today's Internet is primarily the Web, so having "www" is a bit unnecessary.

Many webservers simply aren't configured to properly show the site without the "www".

Answer 2

The World Wide Web had a number of differences from other hypertext systems that were then available:

* The WWW required only unidirectional links rather than bidirectional ones. This made it possible for someone to link to another resource without action by the owner of that resource. It also significantly reduced the difficulty of implementing Web servers and browsers (in comparison to earlier systems), but in turn presented the chronic problem of broken links.
* Unlike certain applications, such as HyperCard, the World Wide Web was non-proprietary, making it possible to develop servers and clients independently and to add extensions without licensing restrictions.

and look WWW has to follow certain standards for browsing like
>hypertext
>resource identifier
>client server model
>markup language

it is not similar for every website to follow such standards now,though it was necesary in 1993-97...if some webside dont follow such standards they can have another wildcards ...and they are quite acceptable in todays internet which is almost going to attain OSI model for networking and internet

Answer 3

Its not necessary to use www in the URL bar. Its accepted as the W3C consurioum has suffixed it..

Answer 4

because this starts most web sites you go to.