Sub-Domains

If we type www.cnn.com into the address bar of our browser to visit the CNN website, then we are using what is known as a subdomain.

TIP: Web hosts can create a subdomain for you within minutes. If they charge you for it, it should only be for the time spent and the additional resources used (disk space etc.),not for "registration" of the name itself!
    
 

The History of Sub Domains

The benefit to sub domains, is for branding purposes. Since a sub domain is looked upon as a new and separate domain, you may have a preference to having cadillac.gm.com instead of cadillac.com. In this case they would be sectioning off the content on a separate domain for branding purposes. The biggest issue with sub domains, is search engines view them as separate sites. Therefore they have the equivalency of separate domains. With a sub domain, you now have to think about developing it as its own entity. This means bringing in inbound links from other web sites. If, for example you have worked hard to bring in 1,000 inbound links to your main domain, you now have to bring in 1,000 links to your sub domains if you expect similar results, and if you have many of them, you are really piling up the workload for yourself. That’s a very simplistic way of looking at it, but it’s usually enough to sway people to avoid sub-domains. Finally, another negative is that links from the sub domain to the main domain will be looked at as inbound links rather than an internal link and therefore will not distribute link juice. There has also been a history of SEO’s and webmasters using sub domains for spam tactics, which is partially what stemmed Google to filter out overly repetitive sub domains returning in search results. Some people prefer to call this a canonical, and we also seen the term third-level domain (the logic is that .com is the top-level domain is the second level, and www is therefore the third).

Machine Names

Subdomains are sometimes used to identify individual computers, each having anans-serif"> Machine Names
Subdomains are sometimes used to identify individual computers, each having anIP address
of its own. In that case, the term machine name is sometimes used instead of "subdomain".

Subdomains For Load Balancing


It is also possible to have multiple subdomains that identify different computers containing the same information This arrangement is often used for extremely busy sites. A visitor types in: "www.busysite.com", and a mechanism called load balancing sends the visitor to one of the available computers (say, "www2.busysite.com" or "www7.busysite.com").

Organizing Information


In most cases, however, subdomains are simply used to organize information with a website. An on-line shop could use the subdomains "books.someshop.com", "flowers.someshop.com", etc., to store related information together. An excellent example of a site that uses subdomains for this purpose is e="font-weight: normal"> About.com If you visit their site, you will notice that they use different subdomains for all of the topics they cover (e.g., "antiques.about.com" and "autorepair.about.com"). Of course, they could have used subdirectories instead ("about.com/antiques/"), but the use of subdomains makes it easy for them to move a topic to a dedicated computer if it turns out to be very popular. For a large, busy site like About, this "scalability" could be an important benefit. For most other sites, however, subdirectories work fine; they need the "200 subdomains" included in some "advanced" hosting packages.

Sub Domains :No Registration Fee


One key point to keep in mind is that, unlike domains, subdomains can be created "at will". For any domain, you can create as many subdomains as you like; you do not to go to a registrar and pay an annual fee.