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5.5.2 Printers

Colour models were dealt with in Subsection 4.7.

You probably also own a printer. Many computers now come with them as part of a package. There are two main types in use today: inkjets and lasers.

InkJet printers work, as their name suggests, by firing tiny droplets of ink at the p
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4.2.4 Keyboards

Every computer comes with a keyboard. They are still the main way of taking text across the boundary into the computer. The one I'm using to type this unit has 109 keys. Under each key is a pressure sensor that detects when the key has been pressed and sends an electronic signal into the computer. There, a small program called the BIOS (Basic Input/Output System) translates the signal into the appropriate numeric code. Other software stores that code in a suitable place in the memory.


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3.5 Digital things

The terms ‘discrete’ and ‘digital’ 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
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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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2.7 Manipulation

As I suggested above, we can change a digital version of some aspect of reality in any way we want. I've used the simple example of tinkering with a digital photograph, but the possibilities for transformation go far beyond this. We can set up elaborate replicas of real-world systems and inspect them in detail. We can establish digital models and run them forward in time to see what might happen in the future. We can even create completely imaginary digital worlds and then explore them as if
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Acknowledgements

All materials included in this unit are derived from content originated at the Open University.

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

1. Join the 200,000 students cur
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8.2 The NOT operation

The NOT operation (note that, as with all logic operators, NOT is always written in capital letters) acts bit by bit on a single binary word according the following rules:

NOT 0 = 1

NOT 1 = 0

In other words, all the 1s in the word are changed to 0s and all the 0s are changed to 1s. Hence, for example,

NOT 1101 1011 = 0010 0100

As you saw earlier, the term complement or 1's complement is sometimes used for the result of the NOT operation. In f
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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.

Please click on the 'View document' link below to read the Numeracy Resource.


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7.3.1 Finding the 2's complement

In Section 2.4 you saw how to find the 2's complement representation of any given positive or negative denary integer, but it is also useful to be able to find the additive inverse of a 2's complement integer without going into and out of denary. For instance, 1111 1100 (−4) is the additive inverse, or 2's complement, of 0000 0100 (+4), but how does one find the additive inverse without converting both binary integers to their denary equivalents?

The answer is that the additive inve
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3.4 Input and output considerations

CCDs are not inherently able to detect colour, only brightness. So it is necessary to rely on the fact that any colour of light can be made up from the three primary colours of light: red, blue and green. (Note that the three primary colours of light are different from the three primary colours of pigments.) Each CCD in the array is therefore overlaid with a red, blue or green filter and so detects the brightness of, respectively, the red light, the blue light or the green light falling on it
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3.1 Introduction

Figure 6
Figure 6 Digital camera displaying image; a memory card is shown alongside

Digital cameras need to represent still pictures digitally,
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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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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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15 Computers and communication systems working together

The combination of communication systems and computers has produced powerful new systems not possible when these technologies are used separately. In section 15–19, I'll be using an ICT system in a supermarket as an example, as it is something that you have probably experienced. The material in this study session is not intended to be a comprehensive examination of how ICT systems are used in supermarkets; I'll just be focusing on some of the supermarket's activities in order to highlight t
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4.2.3 Second computer (the FirstClass server)

The computer on the right of Figure 11 receives the data, manipulates it and then stores it. The computer then typically sends some kind of response back via the network, which may require the computer to retrieve some stored data.

The computer in this example is one of the Ope
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14.1 Introduction

Now that I have introduced you to the processes carried out by a stand-alone computer, I will move on to discuss what happens when computers are linked.


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12.2 Bytes of data

You will recall from Section 6.2 that a binary digit, or bit, can have one of two values: either a 0 or a 1. In a computer, bits are assembled into groups of eight, and a group of eight bits is known as a byte. The abbreviation used for a byte is B, so 512 bytes would be written as 512 B. Although this course will use ‘b’ for bit and ‘B’ for byte, you should be aware that not everyone makes this clear distinction.

A byte of data can represent many different things in a co
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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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10.2 Ports

On the outside of a computer you will see a number of connection points that look like sockets. These sockets are known as ports and they provide connections between the computer and external devices such as a digital camera or printer. Ports control the flow of data between the computer and these devices, ensuring that data is sent and received quickly and reliably.

Modern ICT devices require increasingly large amounts of data to be sent between the computer and the devices. The
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