The supermarket example discussed in Section 1 involves various forms of data that a computer may need to handle. Some of these, such as numbers and characters, are simple but fundamental. Other forms of data, such as sequences, involve more complicated structure. In this section, we will introduce sets, which are a variety of data collection that is different from sequences. But first we will look more carefully at numbers and characters.

When developing software we need to dist
Author(s): The Open University

Multiplication can be thought of as repeated addition. For instance, in denary arithmetic

7 Ã— 5

can be thought of as

7 + 7 + 7 + 7 + 7

There is therefore no need for a new process for the multiplication of binary integers; multiplication can be transformed into repeated addition.

In multiplication the result is very often much larger than either of the two integers being multiplied, and so a multiple-length representation may be needed to hold the result of a mu
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The leftmost bit at the start of a 2's complement integer (which represents the presence or absence of the weighting âˆ’128) is treated in just the same way as all the other bits in the integers. So the rules given at the start of Section 7.1 for adding unsigned integers can be used.

## Example 7

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The number system which we all use in everyday life is called the denary representation, or sometimes the decimal representation, of numbers. In this system, the ten digits 0 to 9 are used, either singly or in ordered groups. The important point for you to grasp is that when the digits are used in ordered groups, each digit is understood to have a weighting. For example, consider the denary number 549. Here 5 has the weighting of hundreds, 4 has the weighting of tens and
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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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There are many types of system â€“ not just ICT systems. For example, we all have a nervous system and, as you are studying T175, you are in a higher education system. Our homes have plumbing systems and electrical systems.

### Activity 1 (exploratory)

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Many of the approaches to planning an ISMS to be found in the literature follow a three-phase, rather than a four-task, approach. For instance, Moses (1994) stipulates seven steps in three phases:

• initiation: the identification of information assets and their security requirements;

• analysis: the identification of possible risks to the security requirements of information assets, of the vulnerabilities to those risks, and
Author(s): The Open University

In this section you will study the process demanded by the British Standard on Information Security Management for planning an information security management system (ISMS). We present ISMS development as a process involving four tasks, each of which may be subdivided into stages. This section also examines the managerial and organisational structures that the Standard recommends to support ISMS development and looks in detail at the ISMS documentation task.

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Modern business theory now views an organisation's intangible, rather than its tangible, assets as the reservoir of much of its value. Even a not-for-profit organisation requires information to be shared and protected for its mission to be accomplished. With this new perspective has come a re-evaluation of the methods to be used to protect the value of an organisation. Historically, four walls were all that was needed to demarcate the inside of an organisation from the outside; and four sturd
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The design of a successful information security policy and strategy for any organisation requires an assessment of a number of key factors. These factors can be categorised as either imperatives or incentives. Imperatives are pressures that force you to act. Incentives are the rewards and opportunities that arise from acting.

In Subsection 3.2 we examine the main imperatives confronting organisations. These arise either from threats to information assets or from the obliga
Author(s): The Open University

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 â€“ paper, for example â€“ and some intangible â€“ 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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This unit introduces you to information security and its management.

A succinct definition of information security might run as follows:

Information security is the collection of technologies, standards, policies and management practices that are applied to information to keep it secure.

But why is it important to secure information? And how should its security be managed? To s
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Diallers are a problem which only affects internet users who have a dial-up connection. A dialler is a type of software mostly used by pornography vendors. Once the dialler software is downloaded and run, you are disconnected from your ISP and connected to another phone number. You are then charged for the use of this number. While diallers do not spy on you, they are malevolent in nature because they can run up huge costs for the victim. They usually connect to a premium-rate phone line, and
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People and organisations can only send spam if they have a collection of email addresses to send to. They â€˜harvestâ€™ these addresses:

• from legitimate company databases;

• from web pages;

• from chat rooms;

• by guesswork;

• from people who use an unsubscribe option.

To minimise the spam you receive:

• Check whether you can set rules
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Some spam mail includes â€˜ADV:â€™ in the title. This indicates that it is part of the system used in the US to allow spam mail but to highlight that it is an advertisement. You can then make an informed choice as to whether to read or delete the message.

ADV: also allows users of email systems that have filtering facilities, such as Outlook, Eudora or Pegasus, to set a rule that will automatically remove the message. The way this works is that some email systems allow you to define a s
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Many spam messages have a line at the bottom offering to unsubscribe you from a mailing list, but you should be very wary of doing this. Quite often the senders of the spam will use the â€˜unsubscribeâ€™ option to verify that your email address is live. They may then sell your address to other people for use in spamming. So using the unsubscribe option can increase your spam rather than reduce it. Our advice is never to use the unsubscribe option unless the mail you receive is from a well-kno
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Unlike a virus, a worm does not infect files on a host computer. Instead it adds a file to the computer that is malicious code, and runs it â€˜in the backgroundâ€™. A computer has many programs running in this way in order for its system to operate. For instance, when you create a document you can see the text editor, such as Microsoft Word, Notepad or Star Office, but in the background the spell checker or the printer program are working even though you do not see them on the screen.

W
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By the end of the unit you should be able to:

• distinguish between different kinds of malicious software (viruses, worms and trojans) and protect yourself against them;

• describe a range of security problems (spam, hoaxes, spyware and adware, homepage hijackers, diallers) and how to deal with them;

• explain the key principles of safety online;

• explain the key principles of keeping children safe online.

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Earlier you saw how a genealogical database records relationships between people. A lineage linked database allows queries such as â€˜Ada Rosewell the daughter of John Rosewellâ€™ and makes possible the creation of family pedigrees and other charts. For example, the pedigree chart below shows how Alcimenes was the son of Jason (the Argonaut) and Medea and the grandson of Aeson and Alcimedes.

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When you submit your query, the search engine will look up each word of the query in the index and construct a list of hits. Hits are pages that contain all of the words in your query.

If you perform an advanced search, additional filters are applied to the hit list. For example, if you search for documents in the .ac.uk domain only, pages from other domains will be excluded from the hit list.

Some search engines provide extra features. Most will check the spelling of the words yo
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