The directory can hold an infinite amount of information.The information is specific to each orginisation that purchases a DSA (Directory System Agent) product, and is only of use within that organisation.Each organisation defines its own data types and data structures.
The International Standards defined data types and structures that all X.500 implementations support,this is so the X.500 is globally integrated.
To get an appreciation of the wide scope of applicability of the X.500 standards users are defining their own specific uses of the Directory.
The growth of the X.500 DIRECTORY (type de for login) was developed for a number of applications.
All of these need a global directory to find an address by using only a name of a supplier ,firm or receipient.So the directory is used to get information on presentation addresses of applications and the capabilities of that application.