Networks

A computer network is a number of computers linked together to allow them to share resources.
Networked computers can share:

• Hardware - such as a printer
• Software - they may be able to load up the same program
• Data - they can load up the same files
  

LANs and WANs

here are two types of network: LAN and WAN.

• A LAN is a Local Area Network covering a small area such as one building e.g. in a school or a college.
• A WAN is a Wide Area Network covering a large geographical area.
  

The Internet is a WAN.
A network of bank cash dispensers is a WAN.
A school network is a LAN. LANs are often connected to WANs, for example a school network could be connected to the Internet.

Telephone lines are often used to connect WANs. LANs use dedicated cables or wireless technology.

Advantages and disadvantages of networks

Advantages

• Sharing devices such as printers saves money.
• Site licences are likely to be cheaper than buying several stand-alone licences.
• Files can easily be shared between users.
• Network users can communicate by email.
• Security is good - users cannot see other users' files unlike on stand-alone machines.
• A file server is easy to back up as all the data is stored in one place.
  

Disadvantages

• Purchasing the network cabling and file servers can be expensive.
• Managing a large network is complicated, requires training and a network manager usually needs to be employed.
• If the file server breaks down the files on the file server become inaccessible. E-mail might still work if it is on a separate server. The computers can still be used as stand alones.
  Viruses can spread to other computers throughout a computer network.
• There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse.
  

A Bus Network

This is the simplest way to connect workstations, servers and other components of a network by using a single cable. One or more of the workstations act as the File Server, whilst the other machines are used as workstations or terminals.

Advantages:

• Cheap
• Easy to install.
  

Disadvantages:

• If there is a problem with the cable, the entire network stops working.
• If many workstations are using the network at the same time, response can be very slow, thus frustrating users who want to work quickly. The technical term for data trying to travel simultaneously along the cable in different directions is called 'data collision'. A busy network will have many data collisions.

A Ring Network

The workstations are attached to a cable arranged in a ring.

Advantages:

• Very fast - all data traffic occurs in the samedirection so there should be no data collisions.
  

Disadvantages:

• If a single machine is switched off then the network does not work. If the cable breaks, once again, the network does not work.
  

A Star Network

Each workstation has its own direct line to the server. Connections to the server are made with hubs or switches.
Hubs connect many lines together.
Switches allow the network manager to connect certain workstations to specific servers.

Advantages:

• Reliable - if one connection fails, it does not affect others.
• Good performance, fewer data collisions as each workstation has its own line.
• Good Security - no workstation can interact with another without going through the server first.
  

Disadvantages

• Expensive to install - lots of cables required.
• Installation is an expert job.
• Extra hardware required such as hubs, switches and wiring centres.
  

Star networks are normally preferred because of their reliability.