TABLE 1: Exchange Server 5.5's Directory Store vs. Win2K's Active Directory
Technology	Directory Store	Active Directory
Underlying database	Jet database engine based	Jet database engine based on
	on database organized in	database organized in 8K pages
	4K pages
Transactional model	Transactions first written into	Transactions first written into
	logs, then later committed to	logs, then later committed to
	database from an in-memory	database from an in-memory
	cache	cache
Online	Supported	Supported
defragmentation
Maximum	Tested to more than	Tested to more than
database size	10 million objects	50 million objects
Filename	dir.edb	ntds.dit
Database utility	eseutil.exe	ntdsutil.exe
Schema	Fixed	Extensible
Replication model	Object-based replication based	Attribute-level replication based
	on a multimaster model;	on a multimaster model;
	configuration and object data	configuration and object data
	replicated to all other servers	replicated to all other domain
	in an organization	controllers within a domain;
		read-only subset replicated to
		Global Catalogs
Replication agent	Single-threaded Directory	Multithreaded replication agent
	Replication Agent (DRA)
Replication transport	Remote procedure calls (RPCs)	RPCs within site; SMTP or RPC
	within site; messaging (i.e.,	messaging between sites; SMTP
	SMTP, RPC, or X.400 intrasite)	for Global Catalog replication
Replication status	Unique Sequence Numbers	USNs on objects and attributes
tracked by	(USNs) on objects	plus server GUIDs