Can you tell me where the Windows NT 4.0 security database (also known as the SAM database) is located on a domain controller (DC)?
The SAM database is part of the registry. It's stored in the HKEY_LOCAL_MACHINE\SECURITY\SAM subkey and duplicated to the HKEY_LOCAL_MACHINE\SAM subkey. At the file-system level, the SAM registry files are stored together with the rest of the registry files under \%systemroot%\system32\config (SECURITY and SAM files).
Also, keep the following in mind, especially if you're worried about unauthorized access to the SAM database. When you back up your NT system, NT also copies the SAM data to your backup media. Likewise, if you create an Emergency Repair Disk (ERD), NT copies the SAM data to the \%systemroot%\repair directory. To provide an extra level of software protection for the security information stored in the SAM database, you can use the Syskey feature.