What's the difference between forum.thinkpads.com and thinkpads.com/forum/

[dcfbf]

My first question is exactly what the heading says
I've just noticed this as I always type "forum.thinkpads.com" into the url bar but "thinkpads.com/forum/" also exists and links here.

Interestingly enough, when I'm on forum.thinkpads.com, the forum button on the top links to forum.thinkpads.com and when I'm on thinkpads.com/forum/, the forum button links to thinkpads.com/forum/ so it seems they are different websites entirely.

My other question is why isn't there just a redirect link from "forum.thinkpads.com" to "thinkpads.com/forum/" to simplify things?

[RealBlackStuff]

The registered website name, a.k.a. domain is: thinkpads.com
The www in www.thinkpads.com is a sub-domain
The forum in forum.thinkpads.com is another sub-domain
The forum in thinkpads.com/forum is a path of a domain
The support in thinkpads.com/support/Thinkpad-Drivers/index.html is a path of a domain
The Thinkpad-Drivers in thinkpads.com/support/Thinkpad-Drivers/index.html is a sub-path of a path of a domain
The index.html in thinkpads.com/support/Thinkpad-Drivers/index.html is a page of a sub-path of a path of a domain

My advice: it's all HTML, so fugeddit.