How does Google Treat Websites with Sub-domains?

Making sub-domains on a domain has now become pretty popular, and many bloggers are now using sub-domains to create custom pages, such as contact and about pages. Although they look professional (and classy :P), they raise a concern. Usually, they are not part of a theme or template, and are custom designed. So some of the on-page SEO elements might be present. And Google Panda and Penguin is said to be domain-level penalty, with one low quality page effecting the whole site. So the popular question arises; how does Google view these sub-domains? And what is the difference, if any, between sub-directory structure and sub-domain structure?

Sub-domains and sub-directories

A sub-domain is an extension of a domain name. But instead of the www prefix, you have your own custom prefix, such as blog.mybloggertricks.com etc. The option to create a sub-domain really is provided by your hosting provider. And those who have the option with their hosting, they take benefit from it, and create sub-domains. You might have seen people having contact pages like contact.domain.com or about.domain.com. This looks professional, which is why many bloggers and webmasters use the option.

(Note: You might be running sub-domain blogs, such as domain.wordpress.com. These sub-domains work differently, so don't get confused)

Sub-directories are folders within your site's main directory. Some people have their blogs or other CMS installed in sub-directories too, such as www.domain.com/blog. This is another way of organizing your site.

But as far as the question of which is better is concerned, it is entirely up to you. Sub-directories are located in a single sub-domain. But there is nothing wrong with having many sub-directories. You can go for what's easy. But I would personally prefer sub-domain structure, because it is easier to implement, and keeps the URLs short(er).

Sub-domain or no?

Now comes the question of what Google thinks. A long time ago, Google only allowed two results from one single sub-domain to appear in search results. Hence, people started making a bunch of sub-domains to make sure most of their content gets into search results. Now, Google considers results from all the sub-domains.

As far as how those sub-domains are treated, well, they get the same treatment the whole website gets. So any malicious software you install on a sub-domain will effect the whole website, so be careful.

Hope I made it clear. You can watch the video by Google above to get a clearer picture. And as always, feel free to ask questions. Cheers :)