WEB Server

Web server can refer to either the hardware (the computer) or the software (the computer application) that helps to deliver Web content that can be accessed through the Internet. 

The most common use of web servers is to host websites, but there are other uses such as gaming , data storage or running enterprise applications.

The primary function of a web server is to deliver web pages on the request to clients using the Hypertext Transfer Protocol (HTTP). This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and scripts.

A user agent, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so. The resource is typically a real file on the server's secondary storage, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includes ways of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting using Active Server Pages (ASP), PHP, or other scripting languages. This means that the  behavior of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this function is used to create HTML documents dynamically ("on-the-fly") as opposed to returning static documents. The former is primarily used for retrieving and/or modifying information from databases. The latter is typically much faster and more easily cached.

Web servers are not always used for serving the World Wide Web. They can also be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring and/or administering the device in question. This usually means that no additional software has to be installed on the client computer, since only a web browser is required (which now is included with most operating systems).

Windows server 2008

Windows Server powers many of the worlds' largest data centers  enables small businesses around the world, and delivers value to organizations of all sizes in between. Windows Server 2012 redefines the server category, delivering hundreds of new features and enhancements spanning virtualization, networking, storage, user experience, cloud computing, automation, and more. Simply put, Windows Server 2012 helps you transform your IT operations to reduce costs and deliver a whole new level of business value.

If we talk about active directory we will realize that active directory is the main object of windows server 2008.
However. active directory cannot work without domain controller in this situation both active directory and domain 
controller have the same important.

Active Diroctory Active Directory (AD) is a directory service  created by Microsoft  for Windows domain windows server   operating systems. Active Directory provides a central location for network administration and security. Server computers that run Active Directory are called domain controller. An AD domain controller   authenticates and authorizes all users and computers in a Windows domain type network assigning and enforcing security policies for all computers and installing or updating software. For example, when a user logs into a computer that is part of a Windows domain, Active Directory checks the submitted password and determines whether the user is a system administrator or normal user.

Domain Controllr

A domain controller is a server that is running a version of the Windows Server® operating system and has Active Directory® Domain Services installed.

What is the key benefit of Microsoft Domain Security?

In a word, single sign-on, or SSO for short. To many, this is the Holy Grail of MS Windows NT and beyond networking. SSO allows users in a well-designed network to log onto any workstation that is a member of the domain that contains their user account (or in a domain that has an appropriate trust relationship with the domain they are visiting) and they will be able to log onto the network and access resources (shares, files, and printers) as if they are sitting at their home (personal) workstation. This is a feature of the domain security protocols.

The benefits of domain security are available to those sites that deploy a Samba PDC. A domain provides a unique network security identifier (SID). Domain user and group security identifiers are comprised of the network SID plus a relative identifier (RID) that is unique to the account. User and group SIDs (the network SID plus the RID) can be used to create access control lists (ACLs) attached to network resources to provide organizational access control. UNIX systems recognize only local security identifiers.

A SID represents a security context. For example, every Windows machine has local accounts within the security context of the local machine which has a unique SID. Every domain (NT4, ADS, Samba) contains accounts that exist within the domain security context which is defined by the domain SID.