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7.4 Multiplying 2's complement integers

Multiplication can be thought of as repeated addition. For instance, in denary arithmetic

7 × 5

can be thought of as

7 + 7 + 7 + 7 + 7

There is therefore no need for a new process for the multiplication of binary integers; multiplication can be transformed into repeated addition.

In multiplication the result is very often much larger than either of the two integers being multiplied, and so a multiple-length representation may be needed to hold the result of a mu
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2.2.3 Positive integers: converting denary numbers to binary

If computers encode the denary numbers of the everyday world as binary numbers, then clearly there needs to be conversion from denary to binary and vice versa. You have just seen how to convert binary numbers to denary, because I did a couple of examples to show you how binary numbers ‘work’. But how can denary numbers be converted to binary? I'll show you by means of an example.

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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
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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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Introduction

Computers are designed to receive, store, manipulate and present data. This unit explains how computers do this, with reference to the examples of a PC, kitchen scales and a digital camera. In particular it explores the idea that the data in a computer represents something in the real world.

This unit is from our archive and is an adapted extract from Computers and processors (T224) which is no longer taught by The Open University. If you want to study formally with us, you may w
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16.1 Introduction

Supermarkets make use of ICT systems for a range of purposes. In the following sections, we'll look at the processes of receiving, storing, retrieving, manipulating and sending data at the checkout, and then we'll move on to the larger context of the supermarket.


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13.2 Magnetic storage

As I mentioned earlier, your computer has a hard disk which provides a permanent storage area for your computer's programs and the files you create. When you save files to your computer's hard disk, you are using a magnetic storage medium. Data stored in magnetic form can be changed once it has been stored, so if you run out of space you can delete some files to make room or, if you want to edit a file, you can make the necessary changes and then save it again. At the time of writing, a mediu
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12.1 Introduction

Data must be stored somewhere when it is not being manipulated. Modern ICT systems require increasingly large amounts of data to be stored for later use, and it is important that the data can be accessed quickly. Data may be stored on the stand-alone computer's hard disk in the form of files.

You may want to move files from one stand-alone computer to another. In addition, you may want to move files from a device, such as a digital camera, to a computer. These activities require some fo
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11.7 Applications

Most people buy computers in order to run applications. There are many different examples of software application, including word processors and spreadsheet, database and graphics packages. Some are combined together in ‘office’ suites, such as the StarOffice applications you can find on the Open University's Online Applications disk.

Word-processing software, such as Microsoft Word, allows you to create, edit and store documents. You can produce very professional-looking do
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11.6 Operating systems

A computer requires software just to look after itself and to manage all its components; this is called the operating system. The operating system handles communication with the other software on the computer and with the hardware resources of the machine, such as the processor and memory. The operating system provides a means of running the computer's application programs. It also provides a standard user interface with windows, buttons and menus so that users can interact with the co
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11.4 Computer software

The electronic components and other equipment that make up your computer system are known as hardware. In order to make the computer do things, such as help you to produce your TMAs, edit photographs or draw diagrams, you also need computer programs, which are called software.


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11.3 Memory

An essential component of a computer is the memory which it uses to hold data currently being used by the processor. This is the random access memory (RAM), the computer's working memory in which programs and data are stored so that they can be accessed very quickly by the processor. The processor stores data in RAM and retrieves data from it as it carries out its manipulations. The more RAM a computer has, the faster the computer programs will run. RAM memory is used and reused and an
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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.


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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
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Introduction

This unit is from our archive and it is an adapted extract from Networked living: exploring information and communication technologies (T175) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area.

This unit will introduce you to some ideas about how information and
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3.7 Databases and XML

In Table 1, it was easy to see which pieces of data belonged to which fields, where the records began and ended, and so on. The tabular layout enabled us to see at a glance the salient features. If you wanted to find a particular name in a table, you ran your eye down the ‘name’ field. It i
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3.6 Viewing the data

Reverting to the relational database we constructed in Section 3.3, you might wonder what, from the user's point of view, has been gained by creating separate tables for the students and courses. With Table 1 you could see at a glance who was studying what. In the relational database it was har
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3.5 Other kinds of data

All the data we have had so far in the database has been text or numbers. I have mentioned that another type of data might be dates. Modern databases, however, can store other kinds of data than text, numbers and dates. They can also store graphics, moving pictures and sounds.

Activity 12 (exploratory)
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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
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