For best search engine benefits what is the best configuration for your blog a subdomain or a subdirectory? First, it is important to clearly identify the difference of a subdirectory versus a subdomain.
Subdirectory example: http://www.mccordweb.com/weblogs/
Subdomain example: http://blog.mccordweb.com
How search engines handle the two is entirely different. So set up determines the link juice and search engine capital that a blogsite will pass to the parent website (in the above example the parent site is mccordweb.com).
Here is a very concise explanation of how search engines index, spider, and count subdomains:
“… Google considers sub domains separate from their parent domains: sub.yoursite.com is considered a different site altogether compared to yoursite.com when it comes to search engine authority.” You can read the full and very interesting article here.
Although you can track subdirectories and subdomains using Google Analytics with special code inserts, how search engine weight and evaluate content that is resides off-domain as in a subdirectory domain is crucial to your organic placement strategy.
It is clear that I am not alone in finding that a subdirectory domain is considered as if it was a separate domain by the search engines. You can find out more by following this thread to the Webmaster World forum.
“It [a subdomain] is treated much more like an independent domain in many respects – for example, if urls from both the root domain and a subdomain show up on the same page of search results, they do not cluster together.”
Matt Cutts says this on the issue:
“My personal preference on subdomains vs. subdirectories is that I usually prefer the convenience of subdirectories for most of my content. A subdomain can be useful to separate out content that is completely different. Google uses subdomains for distinct products such news.google.com or maps.google.com, for example. If you’re a newer webmaster or SEO, I’d recommend using subdirectories until you start to feel pretty confident with the architecture of your site.”
The bottom-line is that a subdomain is simply a way to mask the URL of an off-domain site or blog location and give the APPEARANCE that it is installed within the server where the parent site resides. Search engines consider the content separate and will weight it an index it separately from the parent website. What is crucial to understand is that any links that point to the subdomain blog or website do not flow through and add capital to the parent domain.
For best use of blogging and mini-websites, it is still by far best to install them in subdirectories and not subdomains.