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Module team

The T822 course team

David Reed (Chair and author)

Jill Alger (Editor)

Chris Bissell (Critical reader and author)

Philippa Broadbent (Print buyer)

David Chapman (Author)

Daphne Cross (Assistant print buyer)

Glen Darby (Graphic designer)

Donna Deacon (Course secretary)

Alan Dolan (Course manager)

Roger Jones (Author)

Jo Lambert (Learning projects manager)

Roy Lawrance (Gra
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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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3.3 Hypertext transfer protocol (HTTP)

In this section, I shall look at one example of an application of the TCP/IP protocol suite – sending hypertext pages over the world wide web (WWW or simply the web). However, first I shall very briefly summarise the main features of the web that are relevant to this discussion. There are many sources of information about the web on the web itself for those who want to know more.

In very basic terms, the web is an application of the Internet for accessing resources where
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3.1 What does TCP/IP protocol architecture do?

The Internet is a worldwide public internetwork, which allows computers to communicate with each other even though they may have different manufacturers and different operating systems. The origins of the Internet lie in a project of the US Defense Advanced Research Project Agency in the 1970s, where it was intended to foster communication between research institutions rather than operate for profit. However, a substantial amount of traffic carried by the Internet is now related to com
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2.4 Examples of layer functions

There are several functions that can be performed at one or more of the OSI layers. Some of the more common ones are discussed below.

Connection control

For connection-oriented services, a connection must be established between peer entities. A connection has three phases: connection set-up, data transfer and connection clear. If the peer protocol supports connections, each protocol data unit type corresponds to a primitive type; for instance, a connection request primiti
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1.2 Protocols in multi-service networks: introduction

Early automatic telephone networks were built to carry only voice traffic and to provide a very simple telephone service – now called plain old telephone service (POTS). When computer networks started to appear, either they were separate from telephone networks or the data carried between computers was a small proportion of the traffic on the telephone network. There are various estimates for the growth of voice and data traffic, and various dates have been given for when data traffic will
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5.3 Regaining meaning

Suppose for a minute that the numbers I presented above were generated by a scanner as it produced a bitmap of a photograph. Clearly, the machine on which they are stored will have to get the image back to us by means of a device that can render it into a form meaningful to the human eye – an output device. I shall shortly review such devices. However, there is still work to be done before the computer can pass digitally-encoded data to such a device. For a start it will need to have
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3.1 Ghosts of departed quantities

They are neither finite quantities, or quantities infinitely small, nor yet nothing. May we not call them the ghosts of departed quantities?

(Bishop G. Berkeley, The Analyst)

This section follows up the ideas presented in and aims to:

  • define the terms analogue, discrete and digital;

  • look briefly at the human perceptual system, whic
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2.4.4 Manipulation

Suppose I take a digital photograph of myself for my website. Horrified by my wrinkled, baggy appearance, what can I do? Actually, with the right software I can do more or less anything I like: I can smooth out the wrinkles; I can restore the grey hair to its former splendour; I can even put in a background of books to give me a scholarly appearance. In fact, I can so improve the picture that if you met the real me you probably wouldn't recognise me.

‘Massaging’ my photographic imag
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8.3 The AND operation

The AND operation combines two binary words bit by bit according to the rules

  • 0 AND 0 = 0

  • 0 AND 1 = 0

  • 1 AND 0 = 0

  • 1 AND 1 = 1

In other words, only when both bits are 1 is the result 1. You may find it helpful to think of it this way: when one bit is one and the other bit is 1 the result is 1.

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7.4 Multiplying 2's complement integers

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

7 × 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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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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2.2.2 Positive integers: binary numbers

Just as a denary number system uses ten different digits (0, 1, 2, 3, … 9), a binary number system uses two (0, 1).

Once again the idea of positional notation is important. You have just seen that the weightings which apply to the digits in a denary number are the exponents of ten. With binary numbers, where only two digits are used, the weightings applied to the digits are exponents of two.

The rightmost bit is given the weighting of 2°, which is 1. The ne
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2.2.1 Positive integers: denary numbers

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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Introduction

Computers are designed to receive, store, manipulate and present data. This unit explains how computers do this, with reference to the examples of a PC, kitchen scales and a digital camera. In particular it explores the idea that the data in a computer represents something in the real world.

This unit is from our archive and is an adapted extract from Computers and processors (T224) which is no longer taught by The Open University. If you want to study formally with us, you may w
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16.1 Introduction

Supermarkets make use of ICT systems for a range of purposes. In the following sections, we'll look at the processes of receiving, storing, retrieving, manipulating and sending data at the checkout, and then we'll move on to the larger context of the supermarket.


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13.2 Magnetic storage

As I mentioned earlier, your computer has a hard disk which provides a permanent storage area for your computer's programs and the files you create. When you save files to your computer's hard disk, you are using a magnetic storage medium. Data stored in magnetic form can be changed once it has been stored, so if you run out of space you can delete some files to make room or, if you want to edit a file, you can make the necessary changes and then save it again. At the time of writing, a mediu
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12.1 Introduction

Data must be stored somewhere when it is not being manipulated. Modern ICT systems require increasingly large amounts of data to be stored for later use, and it is important that the data can be accessed quickly. Data may be stored on the stand-alone computer's hard disk in the form of files.

You may want to move files from one stand-alone computer to another. In addition, you may want to move files from a device, such as a digital camera, to a computer. These activities require some fo
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11.7 Applications

Most people buy computers in order to run applications. There are many different examples of software application, including word processors and spreadsheet, database and graphics packages. Some are combined together in ‘office’ suites, such as the StarOffice applications you can find on the Open University's Online Applications disk.

Word-processing software, such as Microsoft Word, allows you to create, edit and store documents. You can produce very professional-looking do
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