Certainly the biggest single change between Windows NT 4 and Windows 2000 is the inclusion in Windows 2000 of an important new service – Active Directory. Active Directory is the native directory service in Windows 2000. Unlike Windows NT 4, when domains were pretty much stand-alone islands that we connected with trust relationships as necessary,
Active Directory is a full-featured directory service. But what is a directory service? Well, a directory service is actually a combination of two things – a directory, and services that make the directory useful. Simply, a directory is a store of information, similar to other directories, such as a telephone book. A directory can store a variety of useful information relating to users, groups, computers, printers, shared folders, and so forth – we call these objects. A directory also stores information about objects, or properties of objects – we call these attributes. For example, attributes stored in a directory for a particular user object would be the user’s manager, phone numbers, address information, logon name, password, the groups they are a part of, and more.
To make a directory useful, we have services interact with the directory. For example, we can use the directory as a store or information against which users are authenticated, or as the place we query to find information about an object. For example, I could query a directory to show me all the color printers in the Frankfurt office, the phone number of Bob in the Delhi office, or a list all of the users accounts whose first name starts with the letter ‘G’. In Windows 2000, Active Directory is responsible for creating and organizing not only these smaller objects, but also larger objects – like domains, organizational units, and sites. In order to fully comprehend what Active Directory is all about, we need to take an initial look at a number of concepts. A deeper discussion on Active Directory will be covered once we get to the AD Implementation and Administration portion of the series.