Topic 4 Communication and Information Systems
In the exam you are expected
to know about:
Applications of communication and information systems
Distributed systems
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Centralised Processing Systems
In the early days of computing, most organisations that could afford a computer had a large central computer called a mainframe. It was called that because of the huge frame that it was built on. Such computers needed large and expensive buildings to house them. Even today we can easily find pictures of huge rooms filled with vast boxes with employees carrying large reels of tape.
Some organisations had minicomputers which, despite the name, were not much smaller or less expensive than the mainframe.
Look at that monitor! Therefore it main sense to have the computer in one place. The terminals that accessed the computer had no computing power at all and were called dumb terminals.
Such a system is called a centralised system. There are some mainframes still in use; they were so damned expensive that the organisations want maximum use out of their investment. The diagram shows a centralised system
Some networks today are centralised with a single file and program server accessed by dumb terminals. The terminals might look like PCs but have no processing power at all.
Another example of centralised processing is the bank automatic teller machine (ATM) that are connected to the bank's central mainframe.
Dispersed Systems
When the microcomputer first started to become popular, many organisations installed them on users' desks. They were stand-alone machines with a complete suite of programs necessary for that individual's or department's work.
Question 1 What are the disadvantages of such an arrangement? ANSWER
Therefore it made sense to link the computers up again in a network. Networks were possible with not only PCs, but also with other forms of microcomputer, for example the BBC, which was popular in many schools.
Local Area Networks (LAN)
Networks have the following advantages:
However the sharing or resources can make the data less secure.
We saw in Module 2 Topic 12 the different types of networks:
We also saw the architecture of networks:
In modern networks the processing power is shared between the server and the PCs throughout the network.
The local area network is connected through a router (pronounced "rooter") to the wide area network. This not a particularly spectacular box shown in the picture below:
The wide area network allows communication between organisations and individuals. We will look at this later.
Distributed Processing
Many organisations have several computers at different locations, linked to each other by networks. This allows for:
This is called distributed processing (not to be confused with dispersed processing. Watch out for this bear trap).
The processing can occur at any of these levels:
Databases can be distributed, which means that the database is stored in more than one physical location. The picture shows the idea:
Question 2 What advantages and disadvantages are there in having a distributed database? ANSWER
The main problem with distributed databases is in keeping the data that are kept on them consistent. This can be achieved by updating the central database each night to reflect the local changes.
In some large databases the central database contains only an index to the locally held data. A query on the central database will identify the location at which the data are held.
Despite the drawbacks (see Question 2), many organisations are moving towards distributed systems to reduce costs, increase efficiency, and to provide best service while not compromising on data integrity and security.
Describe how a distributed database may be implemented. Give an example of an organisation that might hold data in this way. ANSWER
The Internet and the World Wide Web
The Internet started as connections between four military computers in 1967. It has grown immeasurably since then. The World Wide Web is part of the internet that allows you to view pages from participating computers (like you are doing as you read this). Originally these were pages of results for High Energy Particle Physics experiments shared between universities. Professor Tim Berners-Lee is a physicist who invented the language of the web, hypertext mark-up language (HTML). These pages may be linked to others, both within a site and between sites. The two terms are often used interchangeably, although as an ICT professional you should be aware of the difference:
Let us look at how the Internet is made up:
Note that:
When you connect to the Internet, you do so through an Internet Service Provider. For a monthly fee, the ISP provides:
Your computer is connected via a modem (modulator - demodulator). Normal dial-up modems are usually provided as a card that connects directly to the motherboard. If you have broadband, the ADSL modem is a separate box connected via the USB port, although there is no technical reason why it should not be a card in the computer.
Telephone lines have a very poor rate of transmission. A 56 k modem transmits at 56 000 bits per second (yes, bits, not bytes). It would take 26 hours to transmit a 680 Mb CD-ROM. While I write these pages in FrontPage, there is a useful little icon telling me how long it would take this page to transmit at 28 kilobits per second. This page will take 48 seconds, or 24 seconds on a 56 k modem, not too long. It's useful because I don't want each page to take too long, else you, dear reader, will get fed up.
Broadband is much quicker; a page like this will download in about a second (or less if you have high speed broadband. Some areas do not have broadband, or it's available through a wireless transmitter.
Role of Routers and Server
Routers (pronounced "rooter", not to be confused with a woodworking tool, also spelled router, but pronounced "rowter") are computers that connect multiple networks by storing the addresses of the various networks and how to connect to them. They send data in packets. One packet of data from your computer might well go a different route to the next packet of information. Where several networks coincide, there are nodes.
There are different protocols for different networks, which mean that the network operate to different rules. A computer called a gateway is used to convert packets of information from one protocol to another. (It's a bit like languages. German, English and French have differing words and grammatical rules, which can lead to embarrassment. "Mist" in English means a "fog", while in German, "Mist" means "crap". The pop-singer Sting once announced to his German audience that he was hot, "Ich bin warm"; which actually means "I am gay". Accurate interpretation is essential. And it is with different protocols.)
When you link to your ISP, your computer is a client of the ISP server. When you read these pages, you are NOT linked to my computer at home, rather to the server of my web hosting company (I use 1 and 1).
Question 4 Explain why computer networking has developed rapidly over the last fifteen years. Your answer should discuss three factors that have stimulated this development and three implications for society. (SEB past question) ANSWER
Now try the Topic Quiz