Most users look at a server grade hardware and believe that is the server when the fact is that a physical server grade hardware is nothing but a very power full computer with much more capacity when it comes to memory, hard drives and processor. Physical servers are also built to have redundant power supplies and cooling which allows the physical server to run continuously and one of the reasons for their higher cost. A physical server grade hardware can be used as a normal workstation however it is cost prohibitive , thats why we still see practices use a power full computer as acting servers.
A physical server grade computer becomes a server only when server class operating system configured to perform the roles of providing services to other computer (and their users). Just like the physical server the server class operating systems are capable of much more capacity when it comes to memory, hard drives and processor. addtionally the server class operating systems are designed to accept large ammount of connections from users and offer greater seuirty features.
The computer that is a server runs in is also frequently referred to as a server. That machine may be a dedicated server or used for other purposes as well.
In the client/server programming model, a server awaits and fulfills requests from client , which may be running in the same or other computers. A given application in a computer may function as a client with requests for services from other programs and also as a server of requests from other programs.
Servers are often categorized in terms of their purpose. A Web server, for example, is a computer program that serves requested HTML pages or files. A Web client is the requesting program associated with the user. The Web browser in your computer is a client that requests HTML files from Web servers.
Here are a few types of servers, among a great number of other possibilities:
A proxy server is software that acts as an intermediary between an endpoint device, such as a computer, and another server from which a user or client is requesting a service.
A virtual server is a program running on a shared server that is configured in such a way that it seems to each user that they have complete control of a server.