1. Garbage collection is a housekeeping process that is designed to free space within the Active Directory database.
2. In Windows 2000 and in the original release version of Windows Server 2003, this process runs on every domain controller in the enterprise with a default lifetime interval of 12 hours.
3. You can change this interval by modifying the garbageCollPeriod attribute in the enterprise-wide DS configuration object (NTDS) using ADSIEDIT.msc or ldp.exe.
4. The Active Directory (AD) garbage-collection process performs two vital functions.First, it cleans up deleted objects. When you delete an object in AD, the system doesn't immediately delete the object because when replication occurs, a replication partner would recreate the object. Instead, the system uses a tombstone with a finite lifetime to mark the object as deleted. The tombstone replicates to all domain controllers (DCs), and after it expires, the garbage-collection agent deletes the object.
5. The garbage-collection process also performs online AD defragementation.
6. The default tombstone delete lifetime in windows 2000 and 2003 (w/o SP1) is 60 days. In 2003 Sp1, the value is increased to 180 days.