Why do some sites have www. and others don't?

Hello everyone,
I just noticed that in google search, some sites have the www. prefix on the URL while others don't. Now I know that some sites don't work with the www., however some that do are still listed without it. Why is this? Is it the link that google finds your site, whether it's a http://site.com or a http://www.site.com? Kind of pointless question, just interested to know seeing as though I just started promoting my site without the www. prefix, and I would prefer google to list my site with it.

Thanks, Grand.

 

You can tell Google to use or not use the www as a setting on your sitemap page in Google webmaster tools.

 

Ah! So you can. That's cool. Thanks.

 

not to mention that when you register the site with Google you can specify the www or not

 

You can specify through linking to your prefered one too!

 

as a webmaster you can run into problems in you have incoming links to both the www and non www versions of your site...I call it split pagerank....sometimes you visit a site and the www version has different pagerank than the non www version....

you can specifiy it in google sitemaps but they also state that they may not follow your directions...plus you have to account for the other search engines...

use a .htaccess redirect to the www version of your site

Split Pagerank

 

yeah either use dns or htaccess to make sure you only use one

 

Well it depends where in bound links are pointing to and whether or not your using apache, you can also choose in sitemaps an option to have it show one of the two.

 

You know I could never really understand the reason of not having the www.

1 logical reason that comes to mind.

If your url is too big.

eg.
http://this-is-a-big-url-and-www-shoud-be-omitted.com/

u shorten ur url by 4 chars. www.

 

Most people aware about that URL starts with www. When people think about write URL, only first thing come in their mind is WWW. So i would prefer to write www