In AD (OS server 2000,2003 etc) the all the information is stored in NTDS.DIT database
if the server is standalone and not connected to any domain then account information is stored in SAM.
Domain user accounts are created in the User Manager. When an account is created, it is automatically recorded in the SAM of the Principal Domain Controller (PDC), which then synchronises it with the rest of the domain. As soon as an account is created in the SAM of the PDC, the user can log onto a domain from any domain workstation.
Information is stored in Schema of Active Directory.
NTDS.DIT the account information is stored
The Active Directory database is stored on each domain controller in a file called NTDS.DIT
Most of the configuration information (but not all) is stored in the Windows Registry.
NTDS.DIT
User account passwords are not stored in the regedit. The passwords are stored in a hidden file located in Windows. This file you can't see no matter what, you would have to get a third party program to unlock it and grab the information from the file.
when you use copy/cut/paste the information is stored in the clipboard
Your hotmail account will tell you how many email you have stored in your account and how much free space is their in your email box
All active directory data base security related information store in SYSVOL folder and its only created on NTFS partition. B: The Sysvol folder on a Windows domain controller is used to replicate file-based data among domain controllers. Because junctions are used within the Sysvol folder structure, Windows NT file system (NTFS) version 5.0 is required on domain controllers throughout a Windows distributed file system (DFS) forest. This is a quote from Microsoft themselves, basically the domain controller info stored in files like your group policy stuff is replicated through this folder structure
On the Domain Controller.
registry database
Users folder