A. The ntds.dit file contains Active Directory (AD) 
information, and because all domain controllers (DCs) 
replicate AD, you might expect the file to be the same size 
on all DCs. However, you might find differently sized files 
because the database file is created individually on each 
DC, and the data--not the database file--replicates. Thus, 
several factors can lead to files with different sizes: 

Over time, the database can become fragmented. Although 
objects are deleted while the database is online, you can't 
compact the database online (compacting requires a manual 
offline defragmentation). 
If a DC is a Global Catalog (GC), it contains information 
about objects of other domains in the forest, thus making 
it larger than non-GC servers. 
The displayed size of the ntds.dit file is the size of the 
file when you started the DC; if many objects are added and 
you restart one DC, that DC's ntds.dit file size will 
appear larger

in win NT Database is going to store in SAM[security 
accounts manager]and the size of data base is 40MB,That's 
the reason we can create 40 thousand object in winNT


But in win 2000/2003 database is going ot store in NTDS and
the size of the data box is 12MB and it is extendable, In 
win 2003 we can create 1 billion objects