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
16.7 A loyalty card scheme Supermarkets, and other types of retailer, use loyalty cards to encourage customers to use their particular shops. Points are awarded when a customer spends money in the shop. Supermarkets ‘reward’ their customers by converting loyalty card points into vouchers. They may also give them discount vouchers for a range of products. Supermarkets use their loyalty card schemes to collect data about their customers. Data about each customer is held in a large database where each customer i
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
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
8 Computers In sections 8–14, I am going to start by considering a stand-alone computer, which is a computer that is not connected to a network. In this type of ICT system, the key processes are the manipulation and storage of data. I'll be introducing some details about the way that a computer manipulates and stores data. Then I'll be discussing the processes that are carried out by computers when they are linked.
7 Describing an ICT system: conclusion We have arrived at a model of a communication system that illustrates the processes needed for communication. We have also looked at the different kinds of communication link that can be used to convey data, and how to express the rates at which they can convey data. In sections 8–14, we shall be looking at a computer system as an example of an ICT system where data manipulation and storage are the most important features.
6.2 Working with bits You may have met the term bit, perhaps in connection with computers. The term ‘bit’ is also important in communication systems. It is an abbreviation for ‘binary digit’. A binary digit can have just one of two values: it can be either 1 or 0. Pulses can be represented by 1s and 0s, that is, as bits, and so it is convenient to think of streams of 1s and 0s being conveyed along the communications link. The rate at which the 1s and 0s are conveyed is known as the data rat
6.1 Networks Next I'll be looking more closely at the ‘network’ block in Figure 8, and in particular at the links that must be present before communication can take place. I'll introduce you to just a few of the forms that these links can take; links may be physical ones, such as cables, or they
4.1.3 The receiver 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
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
3.1 Introduction Generally, when we talk about communication between humans, we mean one person conveying information to another person. Figure 6 shows a basic model, or representation, of a communication system for getting a message from the sender to the recipient. The diagram shows the sender (User
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
12.1 Home page hijackers A home page hijacker is malicious code, quite often attached to a web page, that resets the home page on your browser to one designated by the writer of the code rather than the one you chose. Although this is a low security threat, at the very least these hijackers cause inconvenience, and may give offence. Because of the covert way in which the hijackers are installed it is difficult to reset your home page to your original choice. Every time you re-start your computer and open the br
4.3 Regulation Increasing demand for wireless technology means that the radio frequencies must be carefully managed and allocated by governments to satisfy all the different users and to prevent interference between them. (You may remember the UK Government's auction of 3G radio licences in Spring 2000 which raised approximately £22.5 billion.) Before transmitting radio signals, organisations must usually obtain a licence permitting them to use a specified frequency or band of frequencies. However, o
4.2 Basic principles of wireless transmission I've never quite lost the sense of wonder at the way information can be transmitted with no visible link between the sender and recipient. When I was a child I used to think that sound came through the wire linking my family's radio to the mains electricity supply (I was born before the days of battery-powered transistor radios) and I couldn't understand why my parents referred to it as ‘the wireless’ – since clearly it wasn't. I now know that the wire simply fed the radio with the elec
3.5 Establishing Ethernet standards The first Ethernet network was developed in the early 1970s, long before the days of the World Wide Web and personal computers (PCs). It was designed by researchers at the Xerox Palo Alto Research Centre in California, USA to connect the Centre's ‘Alto’ computers to an office printer. Ethernet's journey from its modest roots to become the dominant network technology is a fascinating one. One of the main reasons for its success lies with the decision to publish the standard. Standard
2.7 Propagation delay The time taken for a signal to travel from its source to its destination is known as propagation delay. This is derived from the verb ‘propagate’ which in a physics context means ‘spread’ or ‘travel’. The propagation delay depends on a number of factors, including the distance the signal has to travel and the signal's speed. Contemporary physics states that nothing can travel faster than the speed of light (or any electromagnetic wave) in a vacuum which, to the neares
2.6 Modifying the medium to carry the message Earlier we said that we can think of a signal as a deliberate variation in some property of the medium used to convey the data. Such variation needs to be done in a meaningful way. For example, think of the way pulses of light could be used to convey Morse code. (Morse code is a code in which letters and numbers are represented by groups of short dots and long dashes.) The light could be switched on and off so that a short light pulse could represent a dot and a longer pulse a dash. The same
5.4 Conclusion You have seen that although the three products you have looked at are very different types of computer, they all embody the same basic functionality and a version of Figure 3 can be drawn for each product to illustrate this. One feature of the PC is the range of forms of secondary memory it can use, and
5.3 Digital camera The last computer I am going to look at is the embedded computer in a digital camera. Figure 10 shows a picture of a digital camera. The screen of the camera is displaying a picture that has previously been stored in a memory card within the camera. This memory card is not the camera computer's main memory, nor is it the secondary memory used to hold the computer's program; it is a form of removable secondary memory where the computer stores the images taken. Next to the camera in Figur
