3.6 A world of numbers Although we may not all enjoy it, using numbers to count and do arithmetic seems to be a natural human activity. For computers, however, there is nothing but numbers. They were designed from the first to handle numbers and that is still all they do. The cleverness of modern software may make it appear that they do much more, but this is an illusion. The interior world of the computer, the territory inside the boundary, is a world of numbers and nothing else. Some of you may have
3.4 Discrete things In contrast to analogue quantities, which change continuously, discrete quantities change in a series of clear steps. Again, an example should make this clear. In Subsection 3.2, I considered the case of an analogue volume control. A discrete volume control is shown in Author(s):
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
2.5: Crossing the boundary So computers are used to acquire, store and present, exchange, and manipulate interesting characteristics of the world. But this raises a serious problem: the world we inhabit and know so well and the world inside the computer are very different in kind. We live in an analogue world. The world of the computer is digital. The exact meaning of these terms may not be very clear to you at the moment. I will define them both in the next section. For the moment, the only point
Learning outcomes After studying this course, you should be able to: give examples of quantities that are intrinsically analogue, and quantities that are intrinsically discrete/digital define the terms ‘bit’, ‘byte’ and ‘word’ outline how visual information, such as pictures, diagrams and moving images can be expressed numerically inside a computer describe how sounds such as speech and music can be represented inside a computer in terms of
Acknowledgements All materials included in this course 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 4.0 Licence
8.3 The AND operation The AND operation combines two binary words bit by bit according to the rules 0 AND 0 = 0 0 AND 1 = 0 1 AND 0 = 0 1 AND 1 = 1 In other words, only when both bits are 1 is the result 1. You may find it helpful to think of it this way: when one bit is one and the other bit is 1 the result is 1. 7.6 Arithmetic with binary fractions My final point in the preceding section brings home the fact that integer arithmetic is not really suitable when divisions are to be performed. It is also not suitable where some or all of the values involved in the arithmetic are not – or are not necessarily – integers, and this is often the case. In such cases, arithmetic has to be performed on non-integers. The most common representation for non-integers is the floating-point representation that I mentioned briefly in Box 3. You 7.1 Adding unsigned integers
Study note: You may like to have the Numeracy Resource (attached below) to hand as you study Section 7. It offers extra practice with the manipulations, and you may find this useful. Please click on the 'View document' link below to read the Reference Manual. 1 Representing data in computers: introduction A computer is designed to do the following things:
receive data from the outside world;
store that data;
manipulate that data, probably creating and storing more data while doing so;
present data back to the outside world. In the next few sections I am going to examine in more detail the data that a computer receives, stores, manipulates and presents. I 16.2 Processes at the checkout From the point of view of the customer and the checkout operator, a supermarket's ICT system is like the stand-alone computer you saw in Figure 10 in Section 9. The system map in Author(s): 13.3 Optical storage
A CD-ROM (Compact Disk Read Only Memory) uses a laser-based optical form of storage. This type of disk has been used for many years to distribute music and computer software. A CD-ROM drive is needed to read the disks. Data is locked into the disk during manufacture, and cannot afterwards be changed. There are two other types of CD device for computers: CD-R (CD-recordable) and CD-RW (CD-rewritable). With the right sort of CD drive in your computer, you can 'burn' data (that is, 11.1 Introduction A stand-alone computer needs two main components to manipulate data: a processor and a working memory. 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. 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 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 Learning outcomes After studying this course, you should be able to: understand the concept of e-government, and the associated benefits and drawbacks understand how a relational database differs from a flat database, including the function and construction of a joining table understand some of the basic principles of XML understand the basic principles of biometric identification and verification systems identify suitable entities, attr References 6.2.3 Likelihood, impact and risk Having looked at threats, vulnerabilities, outcomes and impacts, we are now in a position to offer a definition of risk with regard to threats to the information assets of an organisation. This definition will lead to an approach to measuring and assessing risk that is consistent with the Standard and with IT Governance: A Manager's Guide to Data Security & BS 7799/ISO 177799 (the Set Book). This systematic approach to risk assessment corresponds to Stage 3 of the ISMS documentation ta 5.4 ISMS documentation In this subsection we shall consider Stages 1, 2 and 8 of the ISMS documentation task. Stage 3 is considered in Section 6. We shall not discuss Stage 9 in this course.
