Exercises on Section 1

Exercise 1

  • (a) How many characters are there in the string “This text.”?

  • (b) Which of the following are integers: 3, 0, 98, 4, –22,Author(s): The Open University

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References

Coffman, K. G. and Odlyzko, A. (1998) ‘The size and growth rate of the Internet’, First Monday, Vol. 3, Issue 10, http://firstmonday.org
ITU-T 1–150 (1999) B-ISDN Asynchronous Transfer Mode Functional Characteristics, ITU-T.
ITU-T X.200 (1994) Open Systems Interconnection – Model and Notation, ITU-T. (Also known as ISO/IEC 7498–1.)

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4.2 ATM layers

In this section I shall briefly review some of the main functions of the ATM layers but I shall not go into too much detail because at this stage we are interested in only the general points about protocols.


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5.5.4 Loudspeakers

Speakers also produce an analogue output. The audio program inside the boundary converts the digital encoding of the sound to a series of electrical pulses that are sent to the speaker, where they cause a cone of stiffened paper (or some synthetic material) to vibrate in and out. This makes the air vibrate in the characteristic sound wave.


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5.1 As to the meaning ...

And this song is considered a perfect gem,

And as to the meaning, it's what you please.

(C.S. Calverley, Ballad)

This short section is devoted to rounding off the discussion so far. In Section 1 I remarked that a digital picture of some set of interesting features of the world is of no value unless we can examine it in some way – in other words, take it back a
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4.15 Summary

This has been a very long section; so congratulations on your persistence!

I've considered in detail how text, pictures, moving pictures, diagrams and sound can all be reduced to numbers and stored inside the boundary in a computer's memory. A persistent theme has been the sheer size of the digital representation that we can get as the result. The need to reduce this amount of digital data, to compress the image, sound or film file we end up with, is taken up in the next unit.
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4.11.1 Digital still cameras and camcorders

These devices are now widely and (fairly) cheaply available. There is no film. You point your camera, take your shot and get a compressed digital image that can be transferred straight onto a computer, where it can be edited or printed. Digital still cameras usually compress their images into JPEG format and store them on a tiny, removable memory card inside the camera; the latest digital camcorders can record in MPEG format, stored on a special tape. Both devices work by means of an electron
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4.4 Introducing pixels

Let's try a simple example. I'm going to take an image, divide it into discrete parts and then transform the result into numbers. I shall use the simple picture of a church shown in Figure 12(a). The process will be exactly the same, whatever image we use.

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4.2.2 Standards

Representations must be agreed if they are to be shared. If different computers used different numbers to encode the same character, people would not be able to read each other's documents. There have to be standards. There are countless computer standards, covering every aspect of information technology, from music and picture encoding to programming language design. And, as you would expect, there are standards which apply to character encoding. You may have wondered why I cho
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2.3 The computer in the world

I want to stress what, for me, is the main point. Computers exist because of our human need to reach out into the world. The computer is a tool which, like all tools, strengthens our ability to reach into, and grapple with, the world. This unit explores:

  • the ways in which computers help us make contact with the world;

  • the many purposes we can achieve once a computer has been used to capture some part of the world.


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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.

4.3 Representing moving images

A moving image is simply a series of still images presented at sufficiently short time intervals that the eye smoothes over the change from one image to the next. In practice, this means the images must change at a minimum rate of around 20 per second; if the rate is lower then the moving image flickers or is jerky. Each still image that goes to make up a moving image is known as a frame.

So far as computers are concerned, moving images are of two types. One type is animations
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Learning outcomes

After studying this unit you will:

  • know what all the terms highlighted in bold in the text mean;

  • know how the following types of data are represented in a computer, and what the limitations of such representations are: positive and negative integers; fractions; analogue physical quantities such as weight; true/false quantities; still pictures; text; moving pictures; sound;

  • know, at an introductory level, what data compression is and why it is useful
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3.2 Problems with flat databases

As a database, Table 1 is messy and inefficient, and does not really qualify as a properly constructed database. For instance, what happens if someone signs up to do four evening classes? To allow for this possibility we could incorporate further fields, such as Course4, Course5 and so on. But
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1.6.1 The role of sound

The use of sound is becoming increasingly common, particularly for the following types of application.

  • Applications where the eyes and attention are required away from the screen. Relevant examples include flight decks, medical applications, industrial machinery and transport. If you are a runner, you may have a heart rate monitor that allows you to monitor how fast your heart is beating. This is often indicated by an auditory beep, which spee
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1.3.5 Using colour to represent information

All UIs need to communicate information. Colour can be particularly effective for this. Table 4 summarises some of the techniques that are available.

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4.3.1 Confidentiality, integrity and availability

To preserve the value of an information asset, an organisation needs to sustain simultaneously its scarcity and its shareability within their respective regions. This is the critical high-level information security goal for any information asset; it is the entire rationale of an information security management system.

To maintain the security of an information asset, an organisation must:

  • either make the information asset unavailable in i
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3.2.2. Legislation

In Chapter 1 of IT Governance: A Manager's Guide to Data Security & BS 7799/ISO 177799 (the Set Book), the section entitled ‘Legislation’ lists the UK legislation that affects the management of information security. One way to appreciate the relevance of legislation to an organisation is to identify the rights and entitlements it establishes and then to establish whether the organisation or its stakeholders have an interest in those rights and entitlements. For each law considered,
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1 What this unit is about

The recent huge increases in ownership of home computers and ever-widening access have been obvious boons to many peoples' lives but, as with many things that improve life, there is a downside. The downside with computers is that software crashes, hardware fails and some Internet users want to cause havoc or vandalise your computer. In this unit we will look at a few of the problems that other people may cause you.

Normally when we talk about malicious software we are referring to virus
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4.2 Index

It is not practical for the search engine to go looking at every page on the Web whenever it receives a search request. Instead, the search engine consults a vast index to the Web. This index is prepared in advance and is stored as a database to make retrieval as efficient as possible. The index of a search site is just like the index of a book – it contains a list of words, each with a reference to the page on which that word was found. The reference to the original page is, of course, a U
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