## SAQ 19

Look at the following set of binary numbers:

00011010 00100011 10001001 10011100 10100011 01001101 10000011 01010100 10001000 00010001 10000110 11110010 â€¦

which we may imagine are stored in the memory of a computer.
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In the past, the work of recording sound and music was carried out by professional recording studios. Before digital technology arrived, recordings were made by picking up sounds on a microphone which converted them to an analogue electrical signal. This signal was then transferred to another analogue medium, such as the grooves of a vinyl record or the changing patterns of metallic atoms on a magnetic tape.

At the start of the digital revolution, analogue to digital conversion, and the
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A better solution is to get some electronic help. A page of text is placed in a scanner, which produces an image of the page using techniques that I will discuss shortly. The image is passed to a computer program called an optical character recogniser (OCR), which detects each letter on the page in turn and transforms it into its digital code. This recognition is an immensely difficult task, requiring very sophisticated software, so OCRs are generally only partially effective.

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In this section I examined the terms analogue, discrete and digital and illustrated their correct use through examples and brief definitions.

I raised the familiar idea of the five human senses which enable us to perceive our analogue world.

Finally I focused on the digital world of counting and representing numbers, and in particular the binary system used in the inner world of the computer.

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Most civilisations have had to face the problem of counting and recording numbers. Our own culture has adopted the so-called Arabic system of numbers. This system is now used more or less worldwide. In this section I will look very briefly at some of its key features.

We have an infinity of numbers at our disposal. If we start counting from 1, we can in theory go on for ever. But although there is an infinity of numbers, we only have a very small, fixed number of digits to
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The terms â€˜discreteâ€™ and â€˜digitalâ€™ are often used interchangeably. For example, The New Penguin Dictionary of Computing contains the following definition.

Digital. Any communication or computing technology whose data may only have a finite number of discrete values.

However, I want you to be clear about the strong association between a digital thing and a number
Author(s): The Open University

2.8 The price

But using computers to acquire, store, exchange and manipulate data comes at a price. By this, I don't mean that the technology is expensive, although this may be an issue. Rather it's the fact that the quality of the information computers give us can often be suspect. More worrying still are the questions of privacy, liberty and security that are raised. The computer gives ordinary people unprecedented access to information. But it also gives people that might not wish us well â€“ gov
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2.6 Going back

Capturing bits of reality and transferring them to a computer would be a pointless exercise if they stayed locked in the digital world. We want access to what we've captured. We want to see the results. In particular, we may want to look at our captive in a different form. For instance, suppose we input the series of temperature readings shown in Author(s): The Open University

1 Aims

In this unit, I want to be more specific and look at the way computers represent and handle data. The unit aims to:

• broaden the definition of a computer and explain the concept of crossing the boundary between the computer's world and our own

• explain the digital nature of the computer's world and contrast it with our analogue world of sense and motion

• describe in detail how to transform features of our world i
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Introduction

This unit introduces the important distinction between our analogue world of colour, sound, taste and touch and the computer's peculiar binary world of digital entities. Concepts of the analogue universe in which we live and the digital world we create are explained. The way in which information, in the form of text, still and moving images, and sound can cross the boundary from the analogue universe into a digital world is explored.

This unit is from our archive and is an adapted extr
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8.4 The OR operation

The OR operation (occasionally called the inclusive-OR operation to distinguish it more clearly from the exclusive-OR operation which I shall be introducing shortly) combines binary words bit by bit according to the rules:

• 0 OR 0 = 0

• 0 OR 1 = 1

• 1 OR 0 = 1

• 1 OR 1 = 1

In other words, the result is 1 when either bit is 1 or when both bits are 1; alternativel
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8.1 Introduction

Study note: You may like to have the Numeracy Resource to hand as you study Section 15. It offers extra practice with the logic operations, and you may find this useful.

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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 â€˜borrowingâ€™ 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 â€˜memory stickâ€™, is a small storage device which is completely external and connects to the computer via a USB
Author(s): The Open University

11.2 The processor

The processor can be thought of as the â€˜brainâ€™ of the computer in that it manages everything the computer does. A processor is contained on a single microchip or â€˜chipâ€™. 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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