PdcChangeLog is an abstract type for a sequence of CHANGELOG_ENTRY objects. The change log is used to support replication of certain Active Directory changes to Windows NT 4.0 operating system BDCs, and is specified in [MS-ADTS] section 188.8.131.52.
The global variable dc for a DC has an associated field dc.pdcChangeLog. When a DC owns the PDCFSMO role, this field contains its change log. As an implementation-specific behavior, other DCs may maintain the dc.pdcChangeLog field as well.