The asynchronous transfer mode (ATM) protocol architecture is designed to support the transfer of data with a range of guarantees for quality of service. The user data is divided into small, fixed-length packets, called cells, and transported over virtual connections. ATM operates over high data rate physical circuits, and the simple structure of ATM cells allows switching to be performed in hardware, which improves the speed and efficiency of ATM switches.

Figure 24 shows the re
Author(s): The Open University

Our universe â€“ everything about us â€“ appears to obey laws, which govern how aspects of the world relate to one another. Scientists refer to these as natural laws, as they seem to be constants of nature, and to distinguish them from laws made by people.

## Exercise 17

Author(s): The Open University

We know that the weather is created by the interaction of earth's atmosphere with the land, the oceans and the energy of the sun. Therefore, the key factors are air pressure, temperature, humidity, wind speed, and so on. Any model will have to identify and represent these properties only, ignoring irrelevant ones such as the current government or the size of the Meteorological Office building. After this, the familiar process of splitting up things can begin.

One successful type of atmo
Author(s): The Open University

Now what about the issue of colour? You should know enough to answer the question without prompting. So far, we've allocated a suitable number of bits to each pixel to give us the range of shade we need. Clearly, then, we must do the same thing to represent colour. But, how many bits will we need to devote to each pixel to represent a useful range of possible colours?

That all depends, of course. It depends on the answers to two questions.

1. How i
Author(s): The Open University

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

The leftmost bit at the start of a 2's complement integer (which represents the presence or absence of the weighting âˆ’128) is treated in just the same way as all the other bits in the integers. So the rules given at the start of Section 7.1 for adding unsigned integers can be used.

## Example 7

Author(s): The Open University

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
Author(s): The Open University

In a supermarket we might see the following data on an item: 5018190009067. On their own, the digits do not mean very much, but these numbers are typical of the type of data input to a computer system. In this instance, they are numbers from a bar code on a jar of coffee. I have described the numbers here as â€˜dataâ€™ because in themselves they do not really tell us anything.

When the bar code is moved past a bar code reader at a checkout counter, the checkout terminal will display det
Author(s): The Open University

We now have two sets of data held by the supermarket: the data about its own products and the personal data about customers. Individually, each of these two sets of information has important uses. However, when they are linked, they provide a very powerful tool for the supermarket.

The personal data from a loyalty card scheme can be used to compile targeted mailing lists, because data about your purchases can help build up a profile of how you spend your money. For example, the supermar
Author(s): The Open University

Personal Digital Assistants (PDAs) or handheld computers are small, portable computers. They each contain a small processor and have specially written operating systems. Two popular types of PDA at the time of writing (early 2005) are those running the Palm OS operating system and those using the Windows Mobile operating system, (also called Pocket PC). There is a range of applications purposely written for PDAs, but many also use special versions of popular applications like Microsof
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

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

Next I'll be looking more closely at the â€˜networkâ€™ 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
Author(s): The Open University

My description of the three subsystems of â€˜means of conveying a messageâ€™ has indicated some important processes that each carries out. These are shown in Figure 8. The key processes are those that will always be carried out and they are shown in bold; the other processes may or may
Author(s): The Open University

You will, perhaps, by now be getting a sense of the challenge of setting up an identification system on a national scale. However, for many routine purposes, establishing who a person is from an entire population of possibilities is not what is required. Instead what is required is confirmation that the person is who they claim to be. This is verification. An example of verification happens when you collect a parcel from a depot. You are sometimes asked to show your driving licence, pa
Author(s): The Open University

Before we start to look at e-government itself, I would like you to read some quotations. During the 1980s and 1990s, the potential of ICT systems for government was discussed by many commentators, but in the UK the official argument for e-government was set out in 1999 in the document Modernising Government. This document, however, is not specifically about e-government. Rather, it is about the much broader issue of how government should be modernised. Here is an extract:

Author(s): The Open University

Pre-recorded digitised speech can be included in a UI relatively easily, but generating speech is harder. One of the methods for synthesising speech is called concatenation. The idea behind concatenation is that the computer stores sentences, phrases or word segments of real human speech. New sentences are constructed by arranging words in the right order. For example, with current telephone directory enquiry systems in many countries, after having made an enquiry of a human operator,
Author(s): The Open University

Modern business theory now views an organisation's intangible, rather than its tangible, assets as the reservoir of much of its value. Even a not-for-profit organisation requires information to be shared and protected for its mission to be accomplished. With this new perspective has come a re-evaluation of the methods to be used to protect the value of an organisation. Historically, four walls were all that was needed to demarcate the inside of an organisation from the outside; and four sturd
Author(s): The Open University

## Activity 8

Reread the short section entitled â€˜Benefits of an information security management systemâ€™ at the end of Chapter 1 of IT Governance: A Manager's Guide to Data Security & BS 7799/ISO 177799 (the Set Book). In light
Author(s): The Open University

Chapter 1 of the Set Book presents a case for effective information security based largely upon perceived threats and legal obligations. Chapter 2 introduces further imperatives, which govern specific types of organisation in the UK.

## Activity 6

Author(s): The Open University