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But there are other reasons. In many ways, a subdomain will be treated as a separate domain and will need to establish its own trust signals. My advice is to use subdomains only when the content involved serves a subtantial and distinct business purpose -- to the degree that you might also at least consider using a separate domain name for the purpose.
[edited by: tedster at 5:32 am (utc) on Jan. 31, 2007]
[edited by: Tastatura at 5:10 am (utc) on Jan. 31, 2007]
For every domain or subdomain you reference in a document your browser has to do an additional DNS lookup to find the IP for that server. This adds round-trip time to the lookup and actually makes the page load slower.
This only relates to the first lookup however, after that its cached and doesnt take anymore time at all. For the best possible optimization you would put all your images and scripts under the www domain and reference them with a full url.
In regard to the initial post, if you create a separate subdomain for every listing you will most certainly get banned from Yahoo and probably google also. Your better off to keep a good ratio of internal pages - subdomains.
I would say just as a rulew of thumb in my experience, try to keep a minimum of 10 pages for every subdomain. (or under every sub-domain)
- once you get over 100 a subdomain is probably a positive move.
I don't think there is any technical basis to support the idea that subdomains load faster than internal pages, in fact, its just the opposite.
In a nutshell, and ignoring for a moment differences between HTTP 1.0 and HTTP 1.1, as well as difference between browsers – browsers, by default, restrict two connections per host. So if your site uses one host, all requests are forced to use two connections. It means that all of the content, images, and other objects are forced two use only two connections. Now picture a page with a lot of images (image gallery) – all of the requests for those objects will go through two connections. Idea behind multiple subdomains is to “spread” that load and allow for more then two connections. If you create CNAMEs for each subdomain, you can “trick” the browser into thinking that it is connecting to multiple servers, so if you have images1.example.com and images2.example.com and image3.example.com you would get 6 connections (vs 2) and that would increase your page load time. Note that I am not talking about improved load time for page where you have a little bit of text and nothing else, but rather page which has a lot of objects.
EDIT - PS:
To post a link or not to post a link...the link is to an interesting study so mods might let it fly - One of the Google's engineers did a study relevant to this subject - Optimizing Page Load Time [die.net]
[edited by: Tastatura at 6:31 pm (utc) on Jan. 31, 2007]
I think the advice about making sure there is substantial content in them is spot on.
If you created a bunch of 1 page subdomains, that would be dodgy. Would it get you in trouble? I don't know if it would now, but probably eventually...
Google considers a subdomain as individual site, for the most part.
The subdomain is unaffected from influence of the top level domain, UNLESS the top level domain links to the subdomain in a prominent manner. [ I.E. About.com ]
When the top level domain links to the subdomain, the subdomain carries the same weight as any page on the top level domain.
If the subdomain is totally separated for the top level domain, its weight is measure by the links pointing directly to the subdomain. [I.E. Blog Hosting Accounts]
As usuall, keywords within the subdomain's name effects rankings.
I hope this made sense.