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The CiscoSecure user database is the database internal to Cisco Secure ACS. The 
CiscoSecure user database draws information from a number of data sources, 
including a memory-mapped, hash-indexed file, VarsDB.MDB (in Microsoft Jet 
database format), and the Windows NT/2000 Registry. The memory-mapped, 
hash-indexed file uses an index and tree structure, so searches can occur 
logarithmically rather than linearly, thus yielding very fast lookup times. This 
enables the CiscoSecure user database to authenticate users quickly. See 

Unless you have configured Cisco Secure ACS to authenticate users with an 
external user database, Cisco Secure ACS uses usernames and passwords in the 
CiscoSecure user database during authentication. If you have configured the 
Unknown User policy, Cisco Secure ACS does not rely on a username and 
password in the CiscoSecure user database for authentication. For more 
information about the Unknown User Policy feature, see the 

. If you have configured specific user accounts 

to use an external user database to authenticate those users, Cisco Secure ACS 
uses information from the specified external user database to perform 
authentication. For more information about specifying an external user database 
for authentication of a user, see the