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2.1 Layers of communication

An internetwork is a network of networks, composed of terminals, switches and communication media. The overall objective of an internetwork is to allow communication between two (or more) networks. This simple description hides the complications that arise in real networks, in which the types of medium vary, transmission errors occur, transmission links fail, switches fail or become congested, equipment is produced by different manufacturers, networks are owned and maintained by differ
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Introduction

People have always communicated with each other – initially by face-to-face communication through gestures and sounds, then over a distance through written messages and signals in the form of fires, lights or flags. Technology, for instance in the form of electrical signals, has reduced many of the limitations of distance. Communication networks have become very important, and modern society depends on them for the smooth operation of economic and social activities. In this unit we regard a
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7 Crossing the boundary – a final word

The real question is not whether machines think but whether men do.

(B.F. Skinner, Contingencies of Reinforcement)

We feel the machine slipping from our hands

As if someone else were steering;

If we see light at the end of the tunnel,

It's the light of the oncoming train

(Robert Lo
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5.5.5 Summary

In this section I've briefly considered the very contentious question of what digital representations mean, but this debate must be left to another course. I have also described some of the devices that take digital information back into the analogue world of sight and sound, presenting it in a form that is meaningful to human eyes and ears.


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9 Conclusion

This unit started with the idea that computers have become an important part of everyday life, especially when all the ‘invisible’ computers that surround us are taken into account – those embedded in objects such as kitchen scales and digital cameras.

Three fundamental ideas introduced in this unit are:

  • computers comprise both hardware (the physical objects) and software (the programs);

  • computers receive data from the ou
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7.5 Dividing 2's complement integers

Just as multiplication can be turned into repeated additions, so division can be turned into repeated subtractions. And just as shifting a binary integer one place to the left equates to multiplying by two, so shifting a binary integer one place to the right equates to dividing by two.

Activ
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7.1 Adding unsigned integers

Study note: You may like to have the Numeracy Resource (attached below) to hand as you study Section 7. It offers extra practice with the manipulations, and you may find this useful.

Please click on the 'View document' link below to read the Reference Manual.

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6 Manipulating data in computers: introduction

Sections 1 to 5 of this unit have shown that in a computer all types of data are represented by binary codes, and that programmers must make sure that the programs they write treat this data appropriately in any particular application: as text if it is intended to be text, as a binary fraction if it is intended to be a binary fraction, and so on.

Programmers must also ensure that the programs manipulate the binary codes in an appropriate way for the particular application. But what sort
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5 Representing data in computers: conclusion

Study note: You will need to refer to the Reference Manual while you are working through this section.

Please click on the 'View document' link below to read the Reference Manual.

2.2.3 Positive integers: converting denary numbers to binary

If computers encode the denary numbers of the everyday world as binary numbers, then clearly there needs to be conversion from denary to binary and vice versa. You have just seen how to convert binary numbers to denary, because I did a couple of examples to show you how binary numbers ‘work’. But how can denary numbers be converted to binary? I'll show you by means of an example.

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17.2 The checkout terminal

The first computer block represents the checkout terminal. The processes at the checkout (receiving, storing, retrieving, manipulating and sending data to the user), are the same as I described earlier. However, the checkout terminal also sends data via the supermarket's network.


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12.2 Bytes of data

You will recall from Section 6.2 that a binary digit, or bit, can have one of two values: either a 0 or a 1. In a computer, bits are assembled into groups of eight, and a group of eight bits is known as a byte. The abbreviation used for a byte is B, so 512 bytes would be written as 512 B. Although this course will use ‘b’ for bit and ‘B’ for byte, you should be aware that not everyone makes this clear distinction.

A byte of data can represent many different things in a co
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11.4 Computer software

The electronic components and other equipment that make up your computer system are known as hardware. In order to make the computer do things, such as help you to produce your TMAs, edit photographs or draw diagrams, you also need computer programs, which are called software.


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7 Describing an ICT system: conclusion

We have arrived at a model of a communication system that illustrates the processes needed for communication. We have also looked at the different kinds of communication link that can be used to convey data, and how to express the rates at which they can convey data. In sections 8–14, we shall be looking at a computer system as an example of an ICT system where data manipulation and storage are the most important features.


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3.1 Tables and flat databases

Databases lie at the heart of many e-government systems, and at the heart of many other ICT systems. The local government websites you looked at in Activity 6, for instance, almost certainly used databases a great deal, as do the majority of central government sites. Away from e-government, the websites for Amazon or eBay, for example, use huge databases.

Constructing a database of any complexity requires careful thought about the way information is organised in any particular context.
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2.3 Styles of presentation

One commodity that is dispensed in vast amounts both by central and local government is information, and so this is one of the more obvious candidates for electronic delivery. Online government services are typically approached via a portal site, which is a kind of entry site from which other sites can be reached. The websites of large organisations, such as Microsoft, the BBC and the Open University, are usually portals.

Going into a portal site is a bit like going into a large
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References

Alberts, Christopher and Dorofee, Audrey (2003) Managing Information Security Risks: The OCTAVE Approach, Addision-Wesley.
Grant, Robert M (1998) Contemporary Strategy Analysis (3rd edn), Blackwell.
Itami, H and Roehl, T (1987) Mobilizing Invisible Assets, Harvard University Press.
Moses, Robin (1992) ‘Risk an
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7 The PDCA cycle

In Section 5 you were introduced to the nine-stage ISMS planning process advocated by the Standard. You have also, in Sections 5 and 6, looked in some detail at some of these stages – those comprising the ISMS documentation and asset identification tasks.

However, an ISMS must not only be planned, it must also be implemented, operated, monitored, reviewed, maintained and improved. Part 2 of the Standard provides guidance on these processes, which it suggests should be undertaken follo
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6.2.2 Threats and vulnerabilities

A hacker who threatens your organisation's information assets is taking advantage of vulnerabilities in the media and systems which handle them. Vulnerabilities and threats clearly go hand-in-hand: each threat is directed at a vulnerability.

The relationship between information assets, threats, vulnerabilities and existing defences is illustrated in Author(s): The Open University

2.1 What is information?

Information comprises the meanings and interpretations that people place upon facts, or data. The value of information springs from the ways it is interpreted and applied to make products, to provide services, and so on.

Many modern writers look at organisations in terms of the use they make of information. For instance, one particularly successful model of business is based on the assets that a firm owns. Assets have traditionally meant tangible things like money, property, plan
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