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7.3 Subtracting 2's complement integers

You will probably have carried out subtraction of denary numbers using rules for subtraction that include the process of ‘borrowing’ whenever you need to subtract a larger digit from a smaller one. It is possible to perform binary subtraction in a very similar way, but that is not what happens in computers. The processor contains the circuits needed to perform addition, and it is much more efficient to use these circuits also to perform subtraction than it is to build in extra circuits to
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2.2 Representing numbers: positive integers

A very straightforward way of finding binary codes to represent positive integers is simply to use the binary number that corresponds to each integer. This is because every positive integer in the everyday number system (known as the decimal or denary system because it uses 10 different digits) has a corresponding number in the binary number system.

As you will see later, in Section 7 of this unit, just as arithmetic (addition, subtraction, etc.) can be performed on everyday denary numb
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16.2.1 Receiving data

In a supermarket ICT system, there needs to be some way for the computer to receive information about the items a customer is buying.

Activity 13 (exploratory)

Think back to a recent visit to your local supermarket and how you ma
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13.4 Flash memory

Flash memory is an electronic form of memory which can be used, erased and reused. A flash memory card is a small storage device used to store data such as text, pictures, sound and video. These cards are used in portable devices such as digital cameras and in small portable computers, such as Personal Digital Assistants (PDAs).

A USB flash memory, sometimes called a ‘memory stick’, is a small storage device which is completely external and connects to the computer via a USB
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11.2 The processor

The processor can be thought of as the ‘brain’ of the computer in that it manages everything the computer does. A processor is contained on a single microchip or ‘chip’. A chip is a small, thin slice of silicon, which might measure only a centimetre across but can contain hundreds of millions of transistors. The transistors are joined together into circuits by tiny wires which can be more than a hundred times thinner than a human hair. These tiny circuits enable t
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9 A stand-alone computer

The computer you are using for your studies is called a personal computer or PC. Although you have an internet connection for use in this course, your computer can probably also be used as a stand-alone computer. Your PC may be a desktop computer or a notebook computer (sometimes known as a laptop computer). Usually a desktop computer comes with separate devices such as a monitor, a keyboard, a mouse and speakers and it runs on mains electricity. Notebook computers
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4.1.2 The network

The network is a communication channel in that it conveys data from the transmitter to the receiver. The network may also manipulate data in some way, and it may also store or retrieve data.

In a mobile phone system, the network conveys the message from User l's handset to User 2's. It will also store the identity of User 1 and the duration of the call. This data is used to work out the amount to charge User 1, which is a form of manipulation of data. A network can be very comple
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2.2.2 Drawing the boundary

Deciding where to place the system boundary is an important consideration in that we have to think about what to include and exclude. This isn't always an easy decision to make and it often depends on the perspective of the person viewing the system.

The system maps in Figures 1
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Introduction

This unit is from our archive and it is an adapted extract from Networked living: exploring information and communication technologies (T175) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area.

Many governments across the world are moving towards the use of infor
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8 Summary

This unit has discussed the importance of information assets to any modern organisation and has made the case for information security management. It has introduced you to extracts from the British Standard on Information Security Management and to the approach advocated in the Standard for establishing and managing an information security management system (ISMS). It has also introduced the PDCA cycle. A particular focus in this unit has been on the planning of an ISMS, and on the four tasks
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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

5.4 ISMS documentation

In this subsection we shall consider Stages 1, 2 and 8 of the ISMS documentation task. Stage 3 is considered in Section 6. We shall not discuss Stage 9 in this unit.


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5.2.1 ISMS documentation

ISMS documentation is carried out at organisation level. Its purpose is to define the scope and context of the proposed system, and the approach to information security management that it will embody. It has five stages: three that initiate the planning process (Stages 1 to 3) and two that complete it (Stages 8 and 9).

  • Stage 1: define the scope of the ISMS The context and scope of the ISMS are defined by considering the nature of the organisa
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3.2.3. Regulation and codes of conduct

Chapter 1 of the Set Book presents a case for effective information security based largely upon perceived threats and legal obligations. Chapter 2 introduces further imperatives, which govern specific types of organisation in the UK.

Activity 6

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2.3 What is information security management?

Information security management is the process by which the value of each of an organisation's information assets is assessed and, if appropriate, protected on an ongoing basis. The information an organisation holds will be stored, used and transmitted using various media, some of which will be tangible – paper, for example – and some intangible – such as the ideas in employees' minds. Preserving the value of information is mainly a question of protecting the media in which it is
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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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13 How do you protect children online?

There is a lot of information available on how to protect younger members of the household, but quite often children know more than their parents and are able to bypass the protection that parents might have installed.

You may view the computer as a major source of information, help, shopping, news, etc. Children like to use it for entertainment, downloading music, accessing chat rooms, playing games (and sometimes even homework). So when considering children's protection the Internet h
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12.1 Home page hijackers

A home page hijacker is malicious code, quite often attached to a web page, that resets the home page on your browser to one designated by the writer of the code rather than the one you chose. Although this is a low security threat, at the very least these hijackers cause inconvenience, and may give offence.

Because of the covert way in which the hijackers are installed it is difficult to reset your home page to your original choice. Every time you re-start your computer and open the br
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9 Adware and spyware

The previous sections of this topic have been concerned with email, but the Internet provides yet more problems, in the form of adware and spyware on the Web. You may have seen pop-up messages on your browser screen offering services or products. What you may not realise is that if you respond to these messages, extra software may be installed alongside other programs without your knowledge.

Adware

Adware is ‘free’ software that is subsidised by displaying adverts


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6.1 Identifying hoaxes

The hoax message relies on the naivety of users in order to mislead them.

  • Do learn more about hoaxes: follow the links below and examine the messages you find. See how convincing they look.

The Good Times Virus hoax

The JDBGMGR.EXE hoax

Both of these messages come from the Electronic Ephemera website, which allows you to search for hoaxes by name or keyword.

Users who fall for these hoaxes can cause problems,
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