They are neither finite quantities, or quantities infinitely small, nor yet nothing. May we not call them the ghosts of departed quantities?

(Bishop G. Berkeley, The Analyst)

This section follows up the ideas presented in and aims to:

• define the terms analogue, discrete and digital;

• look briefly at the human perceptual system, whic
Author(s): The Open University

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
Author(s): The Open University

All materials included in this unit 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 2.0 Licence

1. Join the 200,000 students cur
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

As I indicated at the start of this section, subtraction is converted to addition by replacing the number to be subtracted by its additive inverse, which in the case of binary arithmetic is its 2's complement. An example should make this clear.

## Example 9

Subtract the signed integer 1010 10
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In Section 2.4 you saw how to find the 2's complement representation of any given positive or negative denary integer, but it is also useful to be able to find the additive inverse of a 2's complement integer without going into and out of denary. For instance, 1111 1100 (−4) is the additive inverse, or 2's complement, of 0000 0100 (+4), but how does one find the additive inverse without converting both binary integers to their denary equivalents?

Author(s): The Open University

Sections 1 to 5 of this unit have shown that in a computer all types of data are represented by binary codes, and that programmers must make sure that the programs they write treat this data appropriately in any particular application: as text if it is intended to be text, as a binary fraction if it is intended to be a binary fraction, and so on.

Programmers must also ensure that the programs manipulate the binary codes in an appropriate way for the particular application. But what sort
Author(s): The Open University

Study note: You will need to refer to the Reference Manual while you are working through this section.

CCDs are not inherently able to detect colour, only brightness. So it is necessary to rely on the fact that any colour of light can be made up from the three primary colours of light: red, blue and green. (Note that the three primary colours of light are different from the three primary colours of pigments.) Each CCD in the array is therefore overlaid with a red, blue or green filter and so detects the brightness of, respectively, the red light, the blue light or the green light falling on it
Author(s): The Open University

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
Author(s): The Open University

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
Author(s): The Open University

The introduction of identity cards has proved controversial in several countries, for example France (where identity papers have long been a requirement) and Australia. Generally the issues have related to the questions like: ‘What are these cards actually for?’, ‘Whose interests do they serve?’ and ‘What use will be made of the underlying database of identity data?’ Opponents of identity schemes have pointed out that totalitarian regimes have always found identity systems very us
Author(s): The Open University

Section 5 discussed the ISMS planning and documentation process in general and also went into the details of Stages 1, 2 and 8 of the ISMS documentation task. In this section, we shall discuss Stage 3 of the ISMS documentation task and see how to define a systematic approach to risk assessment. We shall also look at the asset identification task. The remaining two tasks, risk assessment and risk treatment, are outside the scope of this unit.

Author(s): The Open University

The Standard describes the planning of an ISMS, which it refers to as the ‘Plan activity’, as follows.

The Plan activity … is designed to ensure that the context and scope for the ISMS have been correctly established, that all information security risks are identified and assessed, and that a plan for the appropriate treatment of these risks is developed. It is important that all stages of the Plan activity a
Author(s): The Open University

This unit introduces you to information security and its management.

A succinct definition of information security might run as follows:

Information security is the collection of technologies, standards, policies and management practices that are applied to information to keep it secure.

But why is it important to secure information? And how should its security be managed? To s
Author(s): The Open University

It's important to remember that you have the ability to control cookies.

This exercise will take you through setting a level of security on cookies using Microsoft Internet Explorer version 6, while the next page deals with Mozilla Firefox version 1 (you do not have to be online to do this exercise).

Using Internet Explorer

• On the top menu bar of the browser choose Tools > Internet Options.

• <
Author(s): The Open University

Search sites are powered by a search engine: a program that can search for web pages that match your query, and then return a list of hits. The list of hits arrives at your browser as a web page, complete with links to the pages the search engine has found. A website such as the Open University may provide its own search engine which searches only its own web pages, but the big search sites claim to search the entire Web. This is a stunning claim: Google claims to search over four billion web
Author(s): The Open University

In order to show some of the possibilities provided by the Internet, we have gone straight to searching for material online. A careful family historian would take a more measured approach, starting with the evidence to hand within their own family, and researching offline materials as well. Tracing your family tree involves repeating these steps:

• record it

• decide what to pursue next

• <
Author(s): The Open University

As with websites, one of the easiest ways of searching for images is to use a search engine such as Google. You will see that above the Google search box are some words that allow you to select what you are searching for: web, images, groups, news, and more.

What do you do if you don't know the URL of the website you are looking for, or haven't been able to browse to it? The Web is not like a library – it isn't carefully organised and catalogued, and it is growing all the time. Luckily, there are search sites that can help you find what you want.

## 2.3.1 Portals

Author(s): The Open University