Every computer comes with a keyboard. They are still the main way of taking text across the boundary into the computer. The one I'm using to type this unit has 109 keys. Under each key is a pressure sensor that detects when the key has been pressed and sends an electronic signal into the computer. There, a small program called the BIOS (Basic Input/Output System) translates the signal into the appropriate numeric code. Other software stores that code in a suitable place in the memory.

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 NOT operation (note that, as with all logic operators, NOT is always written in capital letters) acts bit by bit on a single binary word according the following rules:

NOT 0 = 1

NOT 1 = 0

In other words, all the 1s in the word are changed to 0s and all the 0s are changed to 1s. Hence, for example,

NOT 1101 1011 = 0010 0100

As you saw earlier, the term complement or 1's complement is sometimes used for the result of the NOT operation. In f
Author(s): The Open University

Study note: You may like to have the Numeracy Resource to hand as you study Section 15. It offers extra practice with the logic operations, and you may find this useful.

Author(s): The Open University

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, 1111Â 1100 (âˆ’4) is the additive inverse, or 2's complement, of 0000Â 0100 (+4), but how does one find the additive inverse without converting both binary integers to their denary equivalents?

Author(s): The Open University

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

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
Author(s): The Open University

A very straightforward way of finding binary codes to represent positive integers is simply to use the binary number that corresponds to each integer. This is because every positive integer in the everyday number system (known as the decimal or denary system because it uses 10 different digits) has a corresponding number in the binary number system.

As you will see later, in Section 7 of this unit, just as arithmetic (addition, subtraction, etc.) can be performed on everyday denary numb
Author(s): The Open University

In a supermarket ICT system, there needs to be some way for the computer to receive information about the items a customer is buying.

## Activity 13 (exploratory)

Think back to a recent visit to your local supermarket and how you ma
Author(s): The Open University

The computer on the right of Figure 11 receives the data, manipulates it and then stores it. The computer then typically sends some kind of response back via the network, which may require the computer to retrieve some stored data.

The computer in this example is one of the Ope
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

You will recall from Section 6.2 that a binary digit, or bit, can have one of two values: either a 0 or a 1. In a computer, bits are assembled into groups of eight, and a group of eight bits is known as a byte. The abbreviation used for a byte is B, so 512 bytes would be written as 512 B. Although this course will use â€˜bâ€™ for bit and â€˜Bâ€™ for byte, you should be aware that not everyone makes this clear distinction.

A byte of data can represent many different things in a co
Author(s): The Open University

The processor can be thought of as the â€˜brainâ€™ of the computer in that it manages everything the computer does. A processor is contained on a single microchip or â€˜chipâ€™. 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
Author(s): The Open University

The computer you are using for your studies is called a personal computer or PC. Although you have an internet connection for use in this course, your computer can probably also be used as a stand-alone computer. Your PC may be a desktop computer or a notebook computer (sometimes known as a laptop computer). Usually a desktop computer comes with separate devices such as a monitor, a keyboard, a mouse and speakers and it runs on mains electricity. Notebook computers
Author(s): The Open University

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
Author(s): The Open University

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
Author(s): The Open University

An important aspect of systems is that each component can be considered as a subsystem. In the health centre appointments system, the â€˜computerised booking systemâ€™ may be a complex system in its own right involving a number of computers networked together. Figure 2 shows
Author(s): The Open University

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.

Many governments across the world are moving towards the use of infor
Author(s): The Open University

A hacker who threatens your organisation's information assets is taking advantage of vulnerabilities in the media and systems which handle them. Vulnerabilities and threats clearly go hand-in-hand: each threat is directed at a vulnerability.

The relationship between information assets, threats, vulnerabilities and existing defences is illustrated in 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