Before getting started with an explanation i would like if you go through following links to get basics of LDAP, AD, ADAM.
Here are the links :
or refer RFC 4511
In simple way i can say that LDAP is just a method to access structured information. Now, what i meant by word structured. Structured information is information in TREE format in case of LDAP.
LDAP uses Client-Server model for communication purpose and this communication happens with message so, we can say that LDAP is message oriented protocol.
You might have a question like what is the need of LDAP . We can store information in database. The reasons are:
1. LDAP local and remote access is standardized whereas this is not the case for database. In database only local access is standardized.
2. LDAP servers are optimized for search operation instead of transactions.
AD is central repository of information. Information about employee,computer,printer etc. AD contain information about all resources and it provides various services like authentication, storage etc. AD is implemented by giant microsoft for windows environment.
AD has various components:
Domain is logical group of resources.
Domain controller is responsible for controlling domain.
Tree is structured representation of domains.
Organisational Unit(OU) represents container for various objects like sales, development, HR.
ADAM stands for Active Directory Application Mode. ADAM is instance of AD.
for example, when we retrieve information from table with few columns and few rows that time we get only some part of table which is known as view. In same way from AD we can take specific part(OU) for ADAM.
ADAM can have multiple instances on single machine which is not possible with AD, this is the reason why ADAM called as AD in application mode. ADAM works as user service not as OS service.
I think this information will help you to get started with LDAP, AD, ADAM. If you need more help or clarification - Add comment.