hai all i am new to seo, i have a site which have 4 services, is that better that i use 4 subdomains for 4 diff services, or just one main domain which has links of this web pages...
It depends. A good example is Yahoo. Yahoo! Mail (mail.yahoo.com), Yahoo! Groups (groups.yahoo.com), Yahoo! Music (music.yahoo.com), My Yahoo! (my.yahoo.com) are Yahoo! services that use different subdomains. If someone searches for "yahoo!", it is possible that all these domains will appear on search results, unlike when they are used as subfolders. So it basically pushes down the competition by displaying related sites on search results.
I have expirienced bad AdSense targeting if subdomains have different content, also it is easier to promote domain then subdomain.Most directories don't allow subdomains websites to be submitted.
Just thought i would let you know that a sub domain is treated as a new domain, however depending on your senario, it still may be benefical.