Networks
Let's start off with some very basic networking terms. This is only a very high level description of networking concepts.
This is a single computer. A single computer is sometimes referred to as a workstation.
This is a computer on which a person (referred to as a user) is running a program (the program is the game Solitaire).
A program runs in the computer's memory on the CPU. The memory and CPU are components contained inside the body of the computer. In the picture above the running program is represented by the word "Solitaire", glowing inside the box at the bottom of the computer picture. The solitaire program communicates with the user by drawing images on the computer's screen.
Two computers hooked together form a network:
The picture above shows the two computers connected by a wire. Specially written computer programs can communicate with each other via that wire. Computers can also be connected via wireless connections.
If two computer programs are communicating with each other over a network connection, and those programs are equal (one program is not dependent on the other), then those programs have a peer-to-peer relationship:
If the relationship between the two programs is not equal -- if one of the programs contains some important resource that the other program needs, that is referred to as a client-server relationship. The program with the resource is the server, and the program that needs the resource is the client. The desired resource is could a collection of web pages (served up by a web server), or a set of files (served up by a file server), email messages served up by an email server, etc. Here is a depiction of a web server serving up information to a web client:
In this picture the computer on the left is running the client program (a web browser such as Firefox or Internet Explorer) and the computer on the right is running a web server. The web server holds several web pages, which is the resource that can be served up to clients. The typical interaction is that the user asks the web browser to display a web page. The web browser contacts the web server and asks it for the page. The web server sends to the page to the browser which then displays it to the user. When the web browser receives the web page, then the page's content is displayed to the user.
Notice that in the picture shown above a user is only shown at the client computer, and no user is directly interacting with the server computer. Since a user can only interact with a server via a client, the server computer is often depicted without a monitor:
A network that that is contained in one physical location is called a local area network (LAN):
For example, if all of the computers in a single college classroom are connected together to form a network, this network would be a LAN.
If two networks are connected together they form an interconnected network (or internet for short):
Notice that the two networks are connected because one computer is on both of the networks. That computer is highlighted below in red. A computer that connects two networks is called a router.
Any two networks that are connected form an internet (small 'i' for internet). The very large, and very famous interconnection of networks that is used worldwide, is called the Internet (large 'I'). The millions of computers that are connected to the Internet are often depicted by a large cloud labeled "The Internet":
