Read the text. It is common to connect computers together to form a network

Networks

It is common to connect computers together to form a network. This is usually done by connecting cables to an electronic board called a network interface card (NIC) in each computer. Networks make communication between users possible and allow software and hardware to be shared. They also make it easier to maintain and control a large number of computers. A network that is connected over a small area – e. g. one building – is called a local area network (LAN), and a network connected over a large area, e. g. different buildings, different cities, or even different countries, is known as a wide area network (WAN). The most common network arrangement is known as a client / server system. The main computers that provide a service on the network are called servers, and the other computers that use the services are called clients.

The physical arrangement of the network is known as the network topology. Three common topologies are known as star, ring, and bus. A star topology has each computer individually connected to a central hub. The hub may be the main server computer, but is more often an electronic device that is used for connecting all the computers together. A ring topology has all the computers connected in a closed loop, and a bus topology has all the computers connected to a main cable that is terminated at each and. A mesh topology, where every computer is connected to every other computer, is not commonly used. Most networks use a mixture of topologies since each arrangement has its own advantages and disadvantages.

Passwords are commonly used to restrict access to a network and keep the system secure. Each user of a network is given an account name and password, which determine what services are made available to them. Passwords are supposed to prevent unauthorized users, or hackers, from breaking into the system, so they must not be easy for outsiders to guess. At the same time, they should not be too difficult for the user to remember. Ideally, they should have a minimum of six characters, and be composed of a mixture of capital and small letters, numbers, and symbols. Certain symbols have to be avoided because they have special meaning in computer systems. It is better not to use words in the dictionary or proper names, since some hackers use special computer programs which automatically try all the words and combinations of words in a computerized dictionary to try to discover or crack other users’ passwords. It is also useful to change passwords frequently.