This security setting determines the number of days' worth of events to be retained for the system log if the retention method for the system log is By Days.
Set this value only if you archive the log at scheduled intervals and you make sure that the Maximum system log size is large enough to accommodate the interval.
Note: This setting does not appear in the Local Computer Policy object.
Computer Configuration\Windows Settings\Security Settings\Event Log
Only Windows XP SP2, Windows Server 2003
Event Log security settings are not registry keys.