3.1.1 Networks
When two or more computers are interconnected this is generally referred to as a network. Networks have become increasingly popular over the last decade. There are a various reasons for this phenomenon. The two main reasons are firstly convenience, and secondly cost savings.
Networks can be used to transfer information between computers, even if they use different operating systems. A network can also be used to send data to remote storage devices and printers, without having to send all of the signals through an expensive mainframe computer. Generally networks provide an inexpensive way to interconnect any number of systems and make communication and sharing of data quick and easy.
There are two main categories of networks used in the industry, which are LAN’s (Local Area Network) and WAN’s (Wide Area Network).
3.2 Local Area Network (LAN’s)
A LAN is a network in which all signals run on a single set of cables, which is fully administered by the owner. There are three typical network topologies (layouts). These are star, ring and bus shapes.
The star shape is the most common. Here outlying stations communicate through a central hub device.
In a ring network, messages circulate the loop, passing from station to station like an old fashioned bucket brigade of fire fighters.
Stations on a bus network send data to a transmitter at one end of the bus. This transmitter rebroadcasts the information back along the bus so that other stations can receive it.
3.2.1 Network Components
Besides the cables linking the computers there are three components that are present in most networks. These are:
The File server This is usually a high performance computer with a very large hard disk. The file server is a mass storage device that all users can share. It is used to store all shared programs and data on the network.
Workstations These are the computers on a network that users work on. Each computer has a network card installed in it, which allows the machine to receive and transmit messages on the network cable.
Shared equipment All users attached to a network can also make use of certain shared equipment.
It doesn’t just end with a single LAN of course. Some companies prefer to keep separate work groups (departments), which is accomplished by giving each work group their own LAN.
3.3 Wide Area Networks (WAN’s)
LANs or MANs that are connected between cities are known as WAN’s. Why do we need WAN’s?
A LAN only has a range of approximately one-kilometre. Even if it could reach further, the cost of laying several hundred kilometres of coaxial cable from one city to another is prohibitively expensive. A better way to link remote computers together is to use a cable network that is already in place and has been carrying long distance messages for years – the telephone system.
To use the telephone system you first need to convert your electronic signal into something more suitable for the phone lines. Telephone transmits sounds, not the radio frequency signals that pulse around a LAN. To do the conversion a device called a Modem is used. The name is a contraction of Modulator-Demodulator. All that means is that the device takes a series of electronic signals and converts them into pulses of sound, which can be sent along the telephone lines.
A prime example of WAN is the Internet. The Internet could be regarded as the largest of all WAN’s. It’s a global network of LAN’s all connected together using the international telephone system. So you can now send messages and data to people in Finland, China or any other country that you can phone.
3.4 Overview of the Internet and the World Wide Web
3.4.1 What is the Internet?
The Internet is a global network of computers that are able to communicate with one another, using a common language called HTML (Hypertext Mark-up Language). These computers are connected
worldwide and can be accessed from anywhere in the world. All you need is a modem and the software to be able to get onto the internet.
The internet is similar to the international telephone system – no one owns or controls the whole system, but it is connected in a way that makes it function as a single big network.
3.4.2 What is the World Wide Web?
Millions of people have Internet access today. The World Wide Web (the web or www) gives you a graphical, easy-to-navigate interface for looking at documents on the Internet. These documents, as well as the links between them, comprise a “web” of information.
The web lets you jump or “hyperlink” from one web page to other pages on the web. You can think of the web as a big library. Web sites are like the books, and web “pages” are like specific pages in the books. Pages can contain news, images, movies, sounds, and 3D worlds – just about anything.
These pages can be located on computers anywhere in the world. When you are connected to the web, you have equal access to information worldwide; there are no additional long-distance charges or restrictions.
Over the last few years, the web has grown to include a vast array of information – everything from stock quotes to job opportunities, bulletin boards to news, previews of movies, literary reviews, and games.
People often talk about “surfing” the web and visiting new sites. “Surfing” means following hyperlinks to pages and subjects you may never have heard about, meeting new people, visiting new places, and learning about things from all over the world.
Remember that the Internet is not just about corporate information. Because it is very easy to publish on the web, many individuals have set up personal “home pages,” pages about themselves and their interests,
pictures of themselves and more. Some even have pointers to what they are wearing in the office that day, or their pet.
As mentioned earlier you can think of the World Wide Web as a big library on the Internet. Web “sites” are like the books in the library and web “pages” are like specific pages in the books. A collection of web pages is known as a web site. You start your journey through the web from a particular web site.
3.5 Browser
A “browser” is a software tool that you use to look at web pages. As you learned, pages on the web are interconnected. You connect to other pages by clicking text or graphics that are called hyperlinks.
3.6 Hyperlinks
Hyperlinks are underlined or bordered words and graphics that have web addresses (also know as URL – Universal Resource Locator) embedded in them. By clicking a hyperlink, you jump to a particular page in a particular web site. You can easily identify a hyperlink. Hyperlink text is a different colour from the rest of the text in a web site.
Surfing the web means following hyperlinks to different web pages. As you surf around the web, you may find pages you have read about or seen mentioned on television. Have fun surfing the web to learn about subjects you are interested in and visiting new sites all over the world.
3.7 Home Pages
A “home page” is the starting point for a web site. It is something like the cover page or the Table of Contents of a book.
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