“example.com” would be the root domain and “www.example.com” would be a subdomain of it, which can either be a separate site, page, or the same as the root domain’s site.
Generally, how many subdomains you can add depends on who runs your nameservers. Most hosts have a limit on how many you can have based on how much you pay.
I don’t know at all about how search engines penalize subdomains.
Well, exampple.com and example.com would be two different domains, but assuming the first was a typo, the www part is just part of the webserver configuration.
Not completely true, subdomains can have their own DNS records that point to completely different IP addresses. However you are correct, if they happen to point to the same machine then the webserver can differentiate them based on what is specified in the Host: header of the incoming HTTP requests.
A couple of other actual commercial examples of non-www prefixes - support.sas.com (which is different from www.sas.com, and www.support.sas.com doesn’t work), and webmail.shaw.ca (which is different from www.shaw.ca, although www.webmail.shaw.ca does resolve but just turns back into www.shaw.ca). Those are just two that I use very frequently; I’ve run into other non-www prefixes before.
Interesting how insistent the board software is about making anything in the www.whatever pattern into a link (even if you delete the [ u r l ] codes in the preview)!
Root is the implied dot at the end of the URL. The “com” (or org, or net, or fr, or what have you) is the “top-level domain” or TLD. What you buy from registrars is the second-level domain, usually just called the domain name (even though that’s not precise, everybody understands what it means).
As to why the ‘www’ appeared there in the first place — in the early days of the Web, it was commonly used to differentiate an institution’s web server from a server that used another protocol. The protocol (on a browser) is indicated in the URL at the very front. E.g. for Hypertext (the one used by the Web) it’s http. Early browsers could often handle other protocols, but the ability to integrate graphics made Hypertext the favorite. Since the Web & http by far dominates modern information servers, the ‘www’ is no longer necessary.
Actually, I’m not sure it was ever strictly necessary; theoretically http://ftp.confusion.gov could resolve to a website, but I don’t think it would actually be done . ( It might be a problem for an ftp program that assumes ‘ftp’, but I’m not sure about that.)
Other protocols used on the internet besides http -
ftp - File Transfer Protocol
gopher - a simple text-based database, based on nested lists. The main competition when the Web was new.
WAIS - Wide Area Information (Search?/Server?) a database to which searches could be submitted.
nntp - news (i.e. Usenet)
smtp - Simple Mail Transfer Protocol; used for e-mail
Note : It’s been a while since I knew this better, so I may have some details wrong; hopefully someone can correct me if need be.
The convention to use ‘www’ arose out of various different ways of indicating such a server with a prefix. MIT has kept the ‘web’ prefix as an alternative all this time, and the following all lead to the same page:
Actually, all major browser can still use other protocols. SSL (accessed via a web address that begins with “https”) is the one most people are familiar with, but ftp and others are still supported.
The first qualifier in an URL has no meaning to the application, be it “ftp” or “boards” or anything else. Only the protocol, specified before the colon, is interpreted.
And, it should be noted while we’re being pedantic about naming conventions, the left-most qualifier in an URL is generally referred to as the host. The host name for web servers is by convention “www” (and “ftp” for FTP servers, etc.), but it doesn’t have to be.