Domains vs subdomains in SEO

I am seeking to understand if search engines treats subdomains as a complete website or as a page of the main domain name. I have a website xxxhttp://portalshops.com and users get web portals using subdomains eg xxxhttp://greg.portalshops.com. Would each subdomain be seen a a link of the main domain name or as an independent website linking to portalshops.com? Please contribute

Google will treat each subdomain as a separate URL. Links to greg.portalshops.com will not have a direct benefit to portalshops.com. However, those links will increase the power of greg.portalshops.com and some of that power will be passed to portalshops.com if a link exists.

Also, if each subdomain has identical content then the user with the greatest amout of power (inbound links) will own most of the SERP listings.

If you created a sub domain for a site that had a high PR would the zero PR of the new sub domain site hurt the PR of the original site?

For example: www.originalsite.com (pagerank 7)

www.subdomain.orginalsite.com (pagerank 0 )

Would it be best not to link the originalsite to the subdomain site while it is building its pr?

Adding a large number of pages to a site will act as a PR sink. It is just like building a wing onto your swimming pool then removing a temporary wall between them - some of the water from the original pool will flow into the new wing - lowering the water level in the original and raising the level in the new.

If you can get adequate links into the subdomain to get it indexed and ranked without drawing upon the resources of the main site that would be a luxury, but why have a subdomain if you are not going to link to it from main site?

IMO, issues other than PR should be considered. How are subdomains ranking in your SERPs, consider all of the new anchor text links that can be exchanged between domain and subdomain.

My preference is to add pages into a new folder on the original domain. I can frequently use them to get double indented SERP listings but the subdomain is not helpful that way.

my personal view, when you add something in your website off topic, maybe a subdomain is a good choice, because it won't hurt your main site, for example build a resource directory which may link to many not themed websites

I think now we are talking here. I have used several resources in this research and seems people have differing opinions about subdomains but one thing seems to be common. That subdomains are treated as seperate websites and may not help much in SE ranking. But there is someone who sent me an email with a rather radical opinion about the forth-coming google trend that we are expecting....-That despite the fact that both domain and subdomain are treated as seperate sites, there is a possible issue with IP addresses. Both of them share similar IP address. His opinion is that in the next google technology which is just around the corner, subdomains might be seen as form of spam in a way. Though am not very aware of what he meant by spam, I find the issue of IP address as a possible trap robots wouldn't fail to see.

About each subdomain having sililar content, with the domain.com, will this not make the both subdomain and domain be treated as one website?