Network Topologies

Networks can be connected in a number of different ways. Each method has its pros and cons.
Bus Networks:
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.

Ring Networks:

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.

Star Networks:

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.

Hardware

Hardware-the physical part of the computer.
Hardware can be put unto 3 catagories:input devices, output devices, and storage devices.

Input devices:Input means to enter data into a computer for processing. An input device is any device that can get data into the computer, i.e Keyboard, joystick, mouse, scanner, etc.

Output devices:once data has been input into a computer and processed, it is of liitle use unless it can be retrived quickly and easily from the system. To allow this, the computer must be connected to an output device, i.e printers, lasers, speakers, etc.

Storage devices:unless you want to lose all of the work you have done on your computer, you must have some means of storing the information, i.e, hard disks, floppy disks, CD ROMs, DVDs, etc.

Copyright

The Copyright Act
This Act was introduced to protect the investment of time, money and effort by the people who create original pieces of work. This can mean authors of books, composers of music, the makers of a film, a computer game designer or a company that creates applications such as word processing software.They all invest a great deal of time and money to produce these things and quite rightly, their work belongs to them.
The Copyright, Designs and Patents Act has two main purposes:

• To ensure people are rewarded for their endeavours
• To give protection to the copyright holder if someone tries to copy or steal their work.

COPYRIGHT AND ICT

As you have seen, the Act protects a wide range of work, both written and computer based.We are more concerned here with the ICT examples. Some of these are:

• Copying software
• Copying or downloading music
• Copying images or photographs from the web
• Copying text from webpages

Software Licences

When you purchase a piece of software you don't actually own the software. What you have purchased is a 'single user licence' for you to be able to use it.

You are able to load your software onto your machine at home and use it for as long as you like. You are not however, allowed to take it to your mates and load it onto his computer - he doesn't have a licence to use it.

Your school or a business needs the same piece of software to be available for many people. They don't buy lots of copies of the software, they buy one copy and will buy either a 'multi-user licence' or a 'site licence'.A multi-user licence allows a certain number of users e.g. 15 to use the software at any one time. When they log off the machine, another 15 can use it.

However, if they allow the software to be used by 16 people at the same time then they are breaking the terms of the licence.A site licence allows everyone on that site or in that office to use the software. It can be loaded onto every machine and people can use it whenever they want.

Viruses

Computer Virus - this is a phrase coined from biology to describe a piece of software that behaves very much like a real virus (only it spreads from computer to computer rather than people!).
What is a computer virus?
A Computer Virus is a computer program that is designed to copy itself repeatedly and attach itself to other computer programs.In the early days of personal computing (1980's) some of the people who created them had a certain misplaced sense of humour. For example, there was a virus that caused all the characters on screen to drop into a heap at the bottom of the display. Very annoying, but relatively harmless. However, quite soon some really nasty versions came out that were deliberately designed to corrupt and delete your files as well as trying to copy itself everywhere.Viruses can cause an immense amount of time wasting and financial loss for people and businesses.For example, the "Melissa" virus was so effective in spreading itself that many huge corporations had to shut down their email systems until the virus could be contained. .It is estimated that there are now around 53,000 computer viruses in existence.
How is a computer virus spread?
The most common way of getting a virus these days is to open an email attachment. Many viruses have been especially designed to take advantage of the way people send emails to each other. Another way is to load an infected file into your computer from some kind of storage device

• floppy disk
• memory stick
• CDROM
• DVD

Note: The CD and DVD products from reputable companies are extremely unlikely to contain a virus. It is the personal 'burned' ones that are a potential problem.It is also possible to pick up a computer virus through what is known as 'peer to peer' file sharing networks. These are internet networks that are used by people to share files amongst each other.There is often no immediate evidence that a virus has been transmitted to a computer, and the user may remain unaware of it until it causes something to go wrong.Basically a virus is spread by allowing it to run (technical term: "execute") on your computer, so any executable file or computer program can contain a virus.

How to guard against viruses

As computer viruses became more of a menace, companies began to develop software to detect and remove them. These became known as anti-virus software.

The Data Protection Act

The Data Protection Act (DPA) was introduced in 1998 and was designed to keep people's information prvate, personal and secure. The DPA only protacts personal information on living individuals and not buissness and companies.
The information can be stored on computer and on paper.
The law was introduced to allow individuals to check whether the information stored is correct. The person in charge of the DPA is the information commisioner.
Within the law/act differnt catagories of people/users:

• Data subjects-person who has the information held about them.
• Data users-People hold the data/information.
• Data Controler-Makes sure the DPA is being followed.

What do Data users have to do?

Must notify the information commisioner and say:

• What data thay want to store
• What they want to use it for
• How long they will keep it for
• who they might pass it on to

They also have to agree to the follow the 8 DPA principles.

• Fairly and lawfuly processed
• Used for limited purposes
• Adiquate and relevate
• Data must be acurate
• Data must not be kept for longer than needed
• Accesible for individual and able to be corrected or removed when nececary.
• Be secure
• Can't be transferd to countries without adiquate protaction.

What rights do Data subjects have?

• See what data is being hald about them, if they ask, however, they might have to pay to be able to see it.
• To change anything that is wrong.
• Right to refuse to have some data to be stored at all if it causes damage or distress.
• Right to refuse process of direct markecting.
• Right to complain Dp commision if rules have been broken.
• Claim compenstaion if you prove damage has been caused.

Expectations

• National security
• Police security
• Exam results

Health and Safety

There are various health problems associated with the regular use of computers, such as stress, eyestrain and injuries to the wrists, neck and back.
Employers must take steps to protect employers whose work involves the regular use of computers.
Eyestrain is the most common of these injuries, if a person is sitting infront of a computerfor long periods of time then he/she will be focusing on the computer screen and this can cause strain to the eyes.
Back problems are also very common because of a persons posture whilst sitting at a computer desk, this is probably due to a poor posture or an awkward postion while sittieng at a copmputer. Mantaing good posture can defeat back problems.

• A fully adjustable chair should avoid poor posture
• Sit with your back straight and head up

Neck problems cane be caused from looking at an awkward postioned monitor so you should position the monitor so that your neck doesn't have to bend too far.

Networks

NETWORKS
A computer network is a collection of computers that have been linked together so that they can communicate with each other. This enables them to share both hardware, software and data.
LOCAL AREA NETWORK
A Personal Computer (PC) at home is often connected to a printer, a modem and maybe even a scanner. All the software needed to run the machine are installed directly onto its hard disk. This is known as a 'stand-alone' machine and is extremely versatile when only one person at a time wants to use the machine or 'peripherals'.

In an office or other large public building such as a school, there are usually many computers in constant use throughout the day. The problems with having many stand alone machines are:

Users cannot easily share information
Every computer needs to be connectedto a printer
Software licences for every machine are expensive
People forget to back up the files they are working on.

With these problems in mind, it was realised at an early stage that connecting these computers together would overcome many of the disadvantages mentioned above. This connection is known as a Computer Network.

When PCs close to one another in a single office or building are joined by a cable, a network is formed known as a Local Area Network (LAN).

Once the computers are connected together into a LAN, many people (users) can share and use the same resources at the same time. They can share files, software, hard disks and peripherals such as a printer or CD-ROM. Users can also use the LAN to communicate with each other by e-mail. Data can be transmitted very quickly between networked computers.

How can you tell whether a computer is networked to other computers?

Usually a networked computer will allow you to send messages to a friend who is working on another computer.
You will probably see messages telling you that you are entering a networked system when you logon.
Sometimes you will see shared resources such as files and software.
Sometimes you will have a choice of more than one printer to send your printouts to
If you have a file server you are also likely to have some space on the server's disk reserved for you to save your work.

WIDE AREA NETWORK
Many modern companies have offices, shops or factories in various locations around the country, and for large corporations, across the world. Even though staff work in different places, they often need to be able to access the same information no matter where they are.

It would not be possible to connect computers in different buildings together using the LAN cables. Imagine how many roads would need to be dug up to lay cables between every single building.

Computers on LANs in one building can be connected to computers on LANs in another building usually through the telephone system, often using a modem. They can also be connected via fibre optic cables, microwave links or satellite.

Workstations and servers:
People connect to the network by using a computer such as a Desktop PC. This machine is often called a 'workstation' or a 'terminal'.
Workstations connect to Servers. These machines can be identical to a Desktop PC but they have a special role to play. They exist to 'serve' and store files to and from the workstations, hence the word, 'Server'. They are often more powerful than a standard PC because they need to store a vast amount of data.

Advantages of Networks:

• Programs can be shared- software packages can be installed onto the file server and accessed by all individual workstations at the same time. This reduces cost, maintenance and makes upgrades easier.
• A user can access any software from any station.
• Data can be shared by all users at the same time. Many people can access or update the information held on a database at the same time. Thus information is up to date and accurate.
• Users can communicate with others on the network by sending messages and sharing files.
• Individual workstations do not need a printer, one high quality printer can now be shared by everyone, thus cutting costs.
• Networks provide security. A user must have the correct Password and User ID in order to be able to access the information on the network.
• Private areas on the network can be set up that allows each user to store their personal files. The only other person who can access these files is the 'system administrator' who looks after the network.

Disadvantages of Networks:

• Networks can be expensive to set up. They often involve taking up floors and ceilings to lay hundreds of metres of cables.
• The File Server needs to be a powerful computer, which often means that it is expensive.
• Networks are vulnerable to security problems. Hackers, disgruntled employees or even competitors might try to break into the system to read or damage crucial information. Much effort is spent preventing unauthorised access to data and software.
• If the main File Server breaks down, then the whole system becomes useless and no-one can carry on working.
• Because networks are often complicated, they need expensive expert staff to look after them.
• As the number of users increase on the network, the performance of the system can be affected and things start to slow down.

On the whole, the advantages of networks outweigh the disadvantages. This is why they are so commonly found in schools, offices and factories. Even home users are starting to use networks to connect PCs around the house.

WELCOME

Welcome to my GCSE revision blogg. I have created this so that i can get into my revision notes from school and home.