All my Drupal web-sites are built on a single installation of Drupal codes. This is commonly known as multisite configuration. One major advantage is that there is only one set of codes to worry about whenever it comes to site maintenance such as program upgrade etc. Those running more than just a handful of sites will appreciate this facility.
Having said that, all my sites above are top level domains. I have tried without success in the past to create sub-domain sites using the same multisite configuration above.
After so many months have passed, I decided to tinker with the idea again. Don't they say never ever give up eh?
It wasn't that straight forward either. I played around with creating sub-domain, domain redirection, creating special folders etc but still not getting what I wanted i.e. getting a sub-domain running under Drupal multisite.