Cambridge IGCSE O-LEVEL-Computer Science

This textbook has been written to provide the knowledge, understanding and practical skills that a student would need for the Cambridge International Examinations Computer Science IGCSE and GCE O Level courses.

As you progress through this book you will begin to realise how complex computer systems really are. By the time you reach Chapter 12 you should have a better understanding of the fundamentals behind computers themselves and the software that controls them

The HEXADECIMAL SYSTEM is very closely related to the binary system. Hexadecimal (sometimes referred to as simply "hex") is a base 16 system and therefore needs to use 16 different "values" to represent each digit.

Data transmission can be either over a short distance (for example, from computer to printer) or over longer distances (for example, over a telephone network). Essentially, three factors need to be considered when transmitting data (each factor has to be agreed by both sender and receiver for this to work without error):

Keeping data safe is extremely important for a number of reasons. It may be personal data that you want to keep within your family or your close friends, or commercial data, such as passwords and bank account details, which need to be kept safe to protect your money.

When data is sent from one device to another, it is important to consider how that data is transmitted. It is also important to ensure that the data hasnt been changed in any way. The internet has now become an integral part of all of our lives. This chapter will consider some of the important technologies going on in the background which support the internet.

Electronic circuits in computers, many new memories and controlling devices are made up of thousands of LOGIC GATES. Logic gates take binary inputs and produce a binary output. Several logic gates combined together form a LOGIC CIRCUIT and these circuits are designed to carry out a specific function.

All modern computers have some form of operating system which users generally take for granted. The operating system makes it possible to communicate with the software and hardware that make up a typical computer system.

Computer systems would be of little real use without a method of input or output. This chapter reviews how a number of input and output devices work. It also considers a variety of applications which make use of these devices.

Computer systems would be of little real use without a method of input or output. This chapter reviews how a number of input and output devices work. It also considers a variety of applications which make use of these devices.

There are many file formats used to store data, be this text, images or sound, in computer systems. This chapter will consider how file compression is used to save memory when storing different types of files. All computer systems have primary memory and secondary memory storage. The main technologies used are magnetic, optical and solid state. Storage devices which use each of these technologies will be described later in this chapter, together with a number of applications.

All modern computers have some form of operating system which users generally take for granted. The operating system makes it possible to communicate with the software and hardware that make up a typical computer system.

People use many different languages to communicate with each other. In order for two people to understand each other they need to speak the same language or another person, an interpreter, is needed to translate from one language to the other language. Programmers use many different programming languages to communicate with computers. Computers only "understand" their own machine code. A program needs to be translated into machine code before it can be "understood" by a computer.

Keeping data safe is extremely important for a number of reasons. It may be personal data that you want to keep within your family or your close friends, or commercial data, such as passwords and bank account details, which need to be kept safe to protect your money.

An ALGORITHM sets out the steps to complete a given task. This is usually shown as a flowchart or pseudocode. Anyone who studies the flowchart or algorithm should be able to work out the purpose of the task.

In order to build a computer system that performs a specific task or solves a given problem, the task or problem has to be clearly defined, showing what is going to be computed and how it is going to be computed. This chapter introduces the tools and techniques that are used to design a software solution that together with the associated computer hardware will form a computer system.

A DATABASE is a structured collection of data that allows people to extract information in a way that meets their needs. The data can include text, numbers, pictures: anything that can be stored in a computer