From Vista onwards, the normal admin you see and use is not really a true admin account. For security reasons, the true admin acc. is disabled and hidden by default. I have never come across a time when I needed or seen a reason to enable it, and I highly recommend leaving it disabled.
Actually its from Windows NT on ward. In Windows NT and greater the True Admin account is denoted with a UID of 500, any user with another UID is a regular user that has special bits set to provide different levels of privileged access to make changes via group policy editor or via domain delegation. In a domain environment the following rules apply:
Local Administrator means the user that is a part of that group can make changes on that computer only regardless of their profile settings.
Domain Admin is a user that make changes on any computer system within a domain.
Enterprise Admin can make changes on any computer system in a domain or part of an enterprise network such as Exchange Servers.
Exchange Server Admins are users that can only make changes on Exchange Servers.
Schema Admins are higher up then Enterprise Admins
Even though these are all admin accounts, there can only be one 500 UID True Admin.