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
Author(s): The Open University

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

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
Author(s): The Open University

6 Manipulating data in computers: introduction

Sections 1 to 5 of this unit have shown that in a computer all types of data are represented by binary codes, and that programmers must make sure that the programs they write treat this data appropriately in any particular application: as text if it is intended to be text, as a binary fraction if it is intended to be a binary fraction, and so on.

Programmers must also ensure that the programs manipulate the binary codes in an appropriate way for the particular application. But what sort
Author(s): The Open University

5 Representing data in computers: conclusion

Study note: You will need to refer to the Reference Manual while you are working through this section.

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
Author(s): The Open University

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
Author(s): The Open University

16.6 Pricing and stock control

A supermarket has a large database of information about its goods, such as the name, price, size and quantity held in stock.

If the price of a particular item changes, the relevant data in the supermarket's database can be easily updated. When the bar code for an item is scanned, the checkout computer searches the database for the item and retrieves the new price. Because the checkout computers are networked, they all use the same data on the database server, so it is not necessary to c
Author(s): The Open University

16.3 Networked computers in the supermarket checkout system

All these processes are very helpful for the purposes of dealing with an individual customer's purchases. However, when computers are linked in a network, many new uses are possible.

Now, I am going to draw a different system boundary. The components of this supermarket checkout system are the checkout terminal, the network and the database server. A database server is used to make the data in databases available to other computers on the network, and therefore to users. You met
Author(s): The Open University

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
Author(s): The Open University

In the block diagram, the computer receives data from the user and sends it into the network. It will manipulate and also store and retrieve data.

If you send a message to a FirstClass conference, your computer receives the message from you as data via the keyboard. The computer manipulates the data into a form that can be sent into the network, in this case the internet via your internet service provider (ISP). Your computer will also store or retrieve relevant data, such as details of
Author(s): The Open University

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.

Author(s): The Open University

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 â€˜bâ€™ for bit and â€˜Bâ€™ 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
Author(s): The Open University

The receiver receives data from the network and manipulates it into a message to send to User 2. Sometimes the receiver may also store or retrieve data.

In the mobile phone communication system, the data received from the network must be manipulated back into sound before being sent to the user. In addition, some mobile phones can store and retrieve data about the user's contacts, so that when a call is received they can translate the phone number of the caller into a name which is then
Author(s): The Open University

4.1.1 The transmitter

The transmitter receives a message from User 1 and manipulates it into data which can be sent into the network. The transmitter may also store or retrieve data relating to the message.

In the mobile phone system, the transmitter, which is User l's mobile phone, receives a message from User 1 in the form of sound. It manipulates the incoming sound into a data format suitable for sending into the mobile phone network. Even basic models of mobile phone handsets can store names and telephon
Author(s): The Open University

2.2 A system map

One way of explaining and analysing a system is to represent it in a graphical form, known as a system map. I'll use the example of a system for making an appointment with a doctor in a health centre to illustrate this point. In this example, the health centre uses a computerised booking system and the patient may phone or visit the health centre to make an appointment. Therefore, the system includes a patient, a receptionist, a doctor, and a computerised booking system. The example sh
Author(s): The Open University

1 Describing an ICT system

In this unit I shall be introducing you to some ideas about how ICT systems work. Because this unit is about ICT systems, I'll be starting with a discussion about what constitutes a system. I'll go on to introduce some diagrammatic ways of representing ICT systems. Then I'll look at some examples to illustrate how they carry out certain processes, namely conveying, storing and manipulating data. You will also find out about other processes performed by ICT systems.

In this sectio
Author(s): The Open University

2.3 Styles of presentation

One commodity that is dispensed in vast amounts both by central and local government is information, and so this is one of the more obvious candidates for electronic delivery. Online government services are typically approached via a portal site, which is a kind of entry site from which other sites can be reached. The websites of large organisations, such as Microsoft, the BBC and the Open University, are usually portals.

Going into a portal site is a bit like going into a large
Author(s): The Open University

10 How to protect yourself against adware and spyware

Steps you can take to protect yourself against this intrusive software.

• If a window appears suddenly, close it using the â€˜Xâ€™ at the top right of the window.

• Never use the â€˜close windowâ€™ option which is sometimes offered in a pop-up window â€“ you never know what is written in the code â€˜behindâ€™ the button or text.

• Even clicking on the â€˜Noâ€™ option to install can have hidden ramifications so the â€˜Xâ€™ i
Author(s): The Open University

4.1.1 Other files