Domain Controller

On Windows Server Systems, the domain controller (DC) is the server that responds to security authentication requests (logging in, checking permissions, etc.) within the Windows Server domain.

In Windows NT, the central domain controller was known as the Primary Domain Controller (PDC), of which there could only be one with this role; all other domain controllers were identified as Backup Domain Controllers (BDC). In Windows 2000 and later the concept of primary and backup domain controllers was eliminated, partially to emphasize the multi-master replication technology available in Windows; however, there are still a number of master roles that only one domain controller can perform: schema master, domain naming master, infrastructure master, Relative ID master, and the PDC Emulator. These are called the Flexible single master operation roles. If one of these roles is lost the domain can still function, and if the server will not be available again the role may be seized. In Windows NT, a BDC can authenticate the users in a domain.

 

Mail Server

A mail transfer agent (MTA) (also called a mail transport agent, message transfer agent, or smtpd (short for SMTP daemon)), is a computer program or software agent that transfers electronic mail messages from one computer to another. The term mail server is also used to mean a computer acting as an MTA that is running the appropriate software. The term mail exchanger (MX), in the context of the Domain Name System formally refers to an IP address assigned to a device hosting a mail server, and by extension also indicates the server itself. An MTA receives messages from another MTA (relaying), a mail submission agent (MSA) that itself got the mail from a mail user agent (MUA), or directly from an MUA, thus acting as an MSA itself. The MTA works behind the scenes, while the user usually interacts with the MUA.  The delivery of e-mail to a user's mailbox typically takes place via a mail delivery agent (MDA); many MTAs have basic MDA functionality built in, but a dedicated MDA like proclaim can provide more sophistication.
 

Database Management System

A DBMS is a complex set of software programs that controls the organization, storage, management, and retrieval of data in a database. A DBMS includes:

• A modeling language to define the schema of each database hosted in the DBMS, according to the DBMS data model.

• Data structures (fields, records, files and objects) optimized to deal with very large amounts of data stored on a permanent data storage device (which implies relatively slow access compared to volatile main memory).

• A database query language and report writer to allow users to interactively interrogate the database, analyze its data and update it according to the users privileges on data.

• A transaction mechanism, that ideally would guarantee the ACID properties, in order to ensure data integrity, despite concurrent user accesses (concurrency control), and faults (fault tolerance).