On completion of this unit you should be able to:
This section, unlike most others in this module, is not based on Accidental Empires. Instead, it aims to provide you with sufficient background knowledge to understand and appreciate the rest of the material. You are not expected to understand the workings of a computer in detail but you will require a knowledge of the various components of a typical computer, and what their functions are. This section will therefore act as your starting point, and the remainder of the module will detail how personal computers (PCs) came to have their present structure and functionality.
In the next segment you will briefly look at the two main categories of technology in the computer industry, namely: Software and hardware
When you think of a computer you probably think of the dull-looking box sitting on top of, or underneath, your desk, plus the monitor, keyboard and mouse. These, along with all of the components inside the computer box, are the physical parts of the computer - the hardware. But the hardware is just an expensive doorstop without something to make it work. For you to produce your annual budget, write your great novel or draw your birthday party invitations you need programs which will make the computer do things. The computer also requires programs just to look after itself and to manage all its components. Programs are the software. Therefore, in this module, when I refer to ‘technology’ I mean both hardware and software, since the computer requires both to be a functional machine.
You might like to think of the hardware as a car, and the software as the driver and the fuel it requires before it can be driven.
Hardware includes components such as the microprocessor, hard disk drive, memory chip, graphics card and so forth. Separate hardware items that are added onto the basic computer unit, such as the monitor, modem, printer, keyboard, etc., are often called peripherals.
Software can be written in a variety of programming languages. A programming language is used to express the instructions which tell the computer what to do in response to a certain action. For instance, word processing software tells the computer to display the letter ‘a’ on the monitor when you press the ‘a’ key on your keyboard. Software can be divided into three basic categories:
Operating systems. These communicate with the hardware of the machine, and act as the basis on which other software programs can be run. The operating system, or OS, is the means by which both other programs and the user interact with the computer. It is the first thing you see when your computer starts up, and it allows you to tell the computer what it is you want to do. Examples of operating systems include DOS, Windows, UNIX and the Macintosh OS. Operating systems are very important in the story of the PC and we shall return to them later.
Languages. These allow developers to write new software programs. There is a wide range of programming languages to suit different types of task; examples include Basic, C, Assembler, Pascal, C++, Visual Basic and Java.
You will look at these in detail if you do a computer programming course, but they do not feature very much in this course.
Applications. These allow you to perform activities to which the computer is suited. Applications are the reason most people buy computers in the first place. Examples include word processors (such as Microsoft Word), spreadsheets (e.g. Lotus 1-2-3), databases (e.g. Access), graphics packages (e.g. CorelDRAW), and so on.
Next you will look at the basic units a computer uses to perform all of its functions. The next segment: Binary, bits and bytes will give you some understanding of what is happening inside your computer.
To appreciate the importance of the various breakthroughs in the history of the computer industry you will need a basic knowledge of how a computer works, and in this segment you will look at how a computer represents information.
At its very lowest level a computer operates by turning on or off millions of tiny switches, called transistors. In computers these transistors can only be in one of two states; that is, on or off. Such devices are thus referred to as two-state devices. Another example of a two-state device might be a conventional light switch. It is either on or off, with no intermediate state. The states of ‘on’ and ‘off’ can be represented by the numbers 1 and 0.
In mathematics the term binary is used to refer to a number system which has only two digits, that is 1 and 0. The number system we use in everyday life has ten digits, 0 to 9, and is called denary. The binary system is the smallest number system that can be used to provide information.
Any number from our normal, denary system can be represented in binary; 0 in denary is 0 in binary. Similarly 1 in denary is 1 in binary. When you get to 2 in denary you have a problem. There are no more symbols in binary; you are restricted to only 1 and 0. So how do you represent two? This question is similar to asking how you represent ten in denary. Once you get to nine you have run out of digits, so you simply create a new column and start afresh, using 1 and 0. This is also what you do in binary, so 2 in denary becomes 10 in binary. When you move on to 3 (in denary) you proceed as before; 3 becomes 11 in binary. The table below shows how denary numbers convert to binary.
|Denary number||Binary equivalent|
It is useful to think of binary in terms of columns. The first column represents units, so a 0 here means no units, i.e. 0, and a 1 means 1 unit. The next column represents the numbers of 2s, so a 1 in this column means 2. The next column represents 4s and so on, with each column being twice as big as the previous one. This is also what we do in denary, each column being a factor of 10 bigger than the previous one. So the denary number 2902 can be interpreted as (2 x 1000) + (9 x 100) + (0 x 10) + (2 x 1). If you want to convert binary numbers to denary, this is a useful method. For instance, if I wanted to convert the numbers 1000100 and 11001 to denary I would make a set of columns as shown.
Conversion of binary numbers to denary
You will not be asked to convert numbers, so don't worry too much about the details. The important thing is to have an idea of what ‘binary’ means.
As I mentioned at the start of this segment, a computer functions by manipulating 1s and 0s. As you have seen, you can represent any denary number in binary. It is also possible to represent any letter of the alphabet, or other character, using binary by simply assigning a code to it in the computer. For instance, there is an agreed representation of text known as International Alphabet Number 5 (IA-5) in which the letter ‘A’ is represented by the binary pattern 1000001. When I type the letter A, this binary number will be stored in my computer. I can later retrieve it and the letter A will be displayed on screen. This will only happen if the computer has received instructions to treat 1000001 as an IA-5 character. The same pattern could be used to represent the denary number 65. The computer knows what to do with the data because it has instructions from a program, and these instructions are themselves binary representations.
It is worth examining the difference between data and instructions. The data is the current information the computer program is working with. This might be some numbers I am adding up, or some text I am typing. It will vary from instance to instance. The instructions are what the computer does with the data. This must always be consistent, for example clicking on the Save button will always save the data.
So numbers and text can be represented using the binary system. What else can? Images can be represented using a technique known as bit-mapping. This divides an image up into thousands of cells and allocates a value to each cell. If the image is in black and white, each cell will have a value of 1 (indicating it is black) or 0 (indicating it is white). Colour can be represented by allocating more information to each cell to indicate the proportion of red, green and blue (RGB) values. A wide spectrum of colours can be created by varying the relative values of red, green and blue. You will encounter bit-mapping in more detail in a later section.
What else can be represented in binary? The answer is just about anything. Sound, like images, can be divided up into different segments and each given an appropriate binary value, which can then faithfully reproduce the sound. This is what your music CD player does.
You will hear people talk about computers being ‘digital’. Sound, light and other natural signals are usually analogue. The difference between digital and analogue is an important one as it underlies the advantage in using computers for many tasks. There is more about what is meant by analogue and digital here: Analogue and digital.
So computers work by manipulating 1s and 0s. These are binary digits, or bits for short. Single bits are too small to be much use, so they are grouped together into units of 8 bits. Each 8-bit unit is called a byte. A byte is the basic unit which is passed around the computer, often in groups. Because of this the number 8 and its multiples have become important in computing. You will particularly encounter the numbers 8, 16, 32 and 64 in various contexts in computing literature, and this is usually due to the 8-bit byte being the basic building unit. The key point to appreciate is that although basing your entire system on only two digits may seem limiting, these two digits can be used to represent almost anything.
You will also hear people speak of kilobytes, megabytes and gigabytes or often just ‘K’, ‘meg’ and ‘gig’ as in, ‘This computer has 64 megs of RAM’, or ‘This file is 45 K’. Bits, bytes, kilobytes and megabytes are merely ways of measuring the size of things computers deal with. A kilobyte is 2 to the power of 10 bytes. This is actually 1024 bytes, but is close enough to a thousand to be given the prefix kilo, meaning a thousand. Similarly, a megabyte is 2 to the power of 20 (or 1 kilobyte squared), which comes out as 1,048,576 bytes. For the sake of convenience, this is called a megabyte, meaning a million bytes. A gigabyte is 1000 megabytes.
Here is an animation in Flash which demonstrates the difference between analogue and digital signals and the conversion from analogue to digital: Flash animation.
In the next segment you will look at the structure of your computer, and what its various components actually do: Computer architecture
In the last segment you saw how a computer could use binary digits (bits) to represent almost any information. This segment will show how a computer uses this binary representation to perform its various tasks.
By combining a series of bytes any data or instruction can be represented. Consider a simple example which takes a number and displays it on the screen. The following instructions might operate for this program:
10000000 = start program
00000001 = exit program
00000011 = consider next byte as a number
00000101 = display previous number
Thus the following stream of bytes would display 10 (2 in denary):
10000000 (program starts)
00000011 (it is told to consider the next byte as a number)
00000010 (treated as a number)
00000101 (it is told to display the previous number)
00000001 (it exits)
This is essentially what computers do, except on a scale of complexity enormously greater than this.
Although computers operate by manipulating 1s and 0s, this is not a very useful way for people to work. A more productive means of telling the computer what to do is required. This need led to the development of programming languages. The first of these was known as Assembler, which operates at quite a low level in the computer, telling the computer where to move data and what to do with it. Assembler takes commands and converts them in to 1s and 0s, which the computer can interpret. Newer programming languages are more sophisticated, and operate at a higher level than Assembler, and their arrival has made the task of programming simpler.
In the dummy program above we used a byte (eight bits) to represent each ‘chunk’ of information. Most computers now use 32 or 64 bits. These chunks are called words and are the basic units the computer manipulates when it is performing an action.
The key to your computer is a chip called the microprocessor. This is its brains, and is where most of the computing takes place.
Before the advent of the microprocessor, computers came mainly in the form of large mainframes which had a different circuit board for each function. At the core of a mainframe computer are three separate units linked together to form what is known as the central processing unit, or CPU. These three units are:
The arithmetic and logic unit (ALU) - this is the unit which does the actual work of the computer. As well as the four basic mathematical functions of addition, subtraction, multiplication and division, it has comparison capabilities such as =, >, < (equals, more than, less than).
The control unit - this unit controls the flow of data from the computer's memory into the ALU and to other devices.
A microprocessor combines the ALU and control unit on one silicon chip, which is why it was at one time referred to as the ‘computer on a chip’. In mainframes the CPU includes memory, but this is separate in microcomputers, so I shall use the term CPU to refer to just the combination of ALU and control unit. I shall describe microprocessors in more detail later, but you should appreciate for now that they can perform a variety of functions. Inside your computer, in addition to the microprocessor which forms the CPU there are other microprocessors that are used to control the graphics card, modem and other devices.
The CPU microprocessor is housed on a circuit board called the motherboard. Also on the motherboard is the clock chip which acts as a metronome for the computer so that all its actions can be synchronized. There may also be one or two ROM chips. ROM stands for Read Only Memory, which means that the data on these chips cannot be altered, it can only be read. These chips often contain some important programs which come supplied with the computer and which are needed for it to function properly. This is why they are made to be read-only; it would be very unfortunate if an unsuspecting user altered them.
As well as the CPU microprocessor there are devices which can be used to enter data into the computer, and which it can use to output data. These are called input/output devices (usually referred to as I/O devices) and might include a keyboard and mouse (for input) and a monitor and printer (for output). The data for these devices will often pass via a slot-in circuit board (called a card) inside the PC which plugs into a slot on the motherboard. These cards perform a number of functions, such as converting data to a form usable by that particular brand of device.
The CPU also sends and receives data to and from the computer's memory, which is usually referred to as RAM (random access memory). The RAM consists of chips similar in construction to the CPU. This is the memory which stores all the data the computer is currently using. You can think of the RAM as the computer's desk. When it needs to work on something it will retrieve it, for example a file from the hard disk, and put it into the RAM - just as you might get a file from a drawer and place it on your desktop. The computer will also load into the RAM the programs it needs to work with this file, in the same way you might place your calculator on your desktop. Like a desktop there is a limit to how much can be placed in the RAM. The contents of RAM are often lost when the computer is switched off.
The microprocessor will also have to read from and write to a permanent data storage device in the form of a hard disk drive. Other permanent storage devices include CD-ROMs (again the ROM in the name indicates that these CDs cannot be written to), optical disks, tape storage or floppy disks (which may be read only or writable).
To receive and send all of this data the microprocessor is connected to cables, which are referred to as buses. This term comes from the Latin omnibus, meaning ‘for all’. Buses are designed to carry all kinds of data, rather like the buses you might use to travel around a city (their name is also derived from omnibus). Thinking of your computer as a street layout, with traffic and buses transporting data to various destinations, is not a bad way of visualizing what is actually happening.
This is a simple overview of a computer's architecture, but it is sufficient for this course. The architecture is summarized in the figure below.
PC Computer Notes - offers information about hardware components and the workings of a computer.
In the next segment you will look at what people mean when they talk about the power of a computer: Computer power
People often talk about the power of a computer. What do they mean by this and what factors affect it?
So what influences the speed and complexity of the computer? There are several factors.
The first factor is the microprocessor chip used for the CPU. Successive generations of chips have more and more transistors placed on them. With more transistors available the chip can be programmed to perform more tasks, therefore increasing its complexity.
Increased numbers of transistors also allow the chip manufacturers to implement new methods of improving memory usage and speed of performance. For example, earlier versions of the Intel microprocessors required a separate chip to be installed in order to cope with any software requiring lots of calculations involving floating point numbers. The extra chip, known as a maths co-processor, was integrated in the main microprocessor as more transistors were made available in subsequent versions.
(The terms ‘floating point numbers’ and ‘maths co-processor’ are explained in the Glossary - you can access this by clicking on the button in the blue sidebar. If you come across terms like these that you don't understand it is worthwhile checking out the Glossary.)
Such improvements in successive generations of microprocessors are typical, and are made possible by the increased numbers of transistors available.
The second factor that determines a computer's power is its clock speed. Each action of the CPU can be thought of as occupying one cycle - although most modern CPUs can perform several tasks at the same time. Therefore the greater the number of cycles per second, the faster the computer.
The third factor is the size of the words that both the microprocessor and the buses can accommodate (go back to the previous segment on computer architecture if you need to refresh your memory about these). You may sometimes hear people refer to a computer - or particularly a games console - as a 32-bit, 64-bit or 128-bit machine. These terms refer to the size of word that the microprocessor can manipulate. The larger the word size, the more information each word can contain. A 32-bit word can contain twice the data of a 16-bit word. Therefore increasing the word size improves both the complexity (more data can be manipulated) and the speed (because it takes the same time to interpret each word).
A fourth factor that affects a computer's power is the amount of memory, or RAM, available. RAM acts as the computer's working memory, so it contains the information the computer needs for its current session. This will include various operating system commands (e.g. what a mouse double click means), the programs currently running (e.g. Microsoft Word with two documents open), current display configurations (e.g. that one Word document is in front of the other and the mouse pointer is in the top left of the screen) and so forth. An increase in the size of the RAM increases the amount of data it can store at any one time. This improves the complexity of the computer because it can run programs that require a lot of data to be handled, and several programs can be run simultaneously. It also increases the speed of the computer because when the RAM becomes full the computer will temporarily store data on the hard disk. This will be retrieved when it is required, which takes more time than having it currently available in memory. So more RAM provides more speed.
The power of computers now is such that their performance is fast enough to meet most needs, and the software you use does not really necessitate the rapid upgrade it once did. This gradual easing of demand poses a problem for the computer industry, and we shall look at its effect on the perception of computers later in the module.
In the next segment you will look at the different types of computer, including PCs: Types of computer
This module is mainly concerned with computers based on microprocessors, called microcomputers or personal computers (PCs). Later sections of this module will examine the PC in detail and the types of software used by them. There are other types of computer though, and you will need to be aware of these. However, don't get too bogged down in the details - the important thing is that you have an appreciation of the different types of computers and the tasks they might perform.
A mainframe computer
Mainframes were the dominant form of computing before microcomputers. They are usually very expensive, powerful and operate specialist software.
Mainframes are typically used by large companies, public authorities and universities for their data handling tasks. These tasks are typically:
File maintenance: This is perhaps the most common use of mainframes. Maintaining records is a huge task for institutions. Records can contain information on sales, credit card status, payroll details, social security details, health records, stock inventory, etc. These either need to be accessed by different people in real-time (for instance a travel agent booking an airline ticket) or updated in batches (for instance warehouse stock levels at the end of each day). It is necessary in such cases to have the data stored centrally and then accessible by those who need it. A lot of minicomputers are now capable of performing these tasks in medium-sized companies.
Simulations: Many physical and engineering problems cannot be solved without the help of complex computer simulations. These require intensive mathematical work, and so take advantage of a mainframe's computational power. Examples include weather forecasting, or calculating the position of astronomical bodies with extreme accuracy. Many minicomputers or workstations are now used for this type of problem.
General purpose: Many universities used a mainframe to act as a general purpose computing facility. Each user can then be given their own area on the mainframe to store files, and different departments can use its resources to perform different tasks, e.g. predicting bird populations in the Biology department and calculating metal stress in the Engineering Department. PCs are now used to perform many of these tasks.
You will have noticed that after each task I mentioned that other types of computer could now be found performing these tasks. This indicates that the general growth in the mainframe area has slowed and is even in decline, as smaller computers have become more powerful. Mainframes are still required by many institutions, however, to perform large data handling tasks. They are particularly useful when data needs to be held centrally, with different people needing access to it. This is illustrated below:
Use of a central mainframe
Minicomputers are powerful, special-purpose computers. They were originally viewed as small mainframes - hence the prefix ‘mini’. However, they have become increasingly powerful and have replaced mainframes for many functions. Examples include Digital Equipment's VAX machines and IBM's AS/400s.
Tasks minicomputers might be used for include:
Plant control: Many industrial plants require a central computing facility to collect data from various sensors and then to act accordingly. For example, in a chemical engineering plant, as the pressure in one vat increases the computer registers this, and opens a release valve slightly while also adjusting the boiler temperature.
Network control: Many computer networks need a central computer which provides storage space and controls the network using special network software. This is known as a server. The other computers which access the server are called clients. Such machines can also act as the interface to the Internet, accepting Internet messages and hosting e-mail and World Wide Web facilities. Powerful PCs can also be used to perform these functions.
Databases: As mentioned above, the role of mainframes in file maintenance is increasingly being taken by minicomputers. Minicomputers can hold databases of records which appropriate people can access.
For the general public it is PCs which tend to symbolize computers. However, most ‘heavy duty’ computing is performed not by PCs but by minicomputers. With the growth in networking computers in most institutions the role of minicomputers has grown. It is in this market that some of the largest software companies, such as Novell who provide networking software and Oracle who supply database software, do most of their business.
The network model is shown below.
The network computing model
Workstations are based on specialized microprocessors and can be thought of as powerful PCs. They are typically used for specialist engineering tasks. Workstations use a special type of microprocessor known as a RISC (reduced instruction set computer) chip. This technology, developed at IBM, removes many of the complex instructions from a microprocessor and has instead a set of basic instructions, which perform their tasks very quickly. This approach increases the speed and the power of the microprocessor, particularly when dealing with numerical problems. The workstation market is dominated by SUN Microsystems. They typically cost in the £10,000s, and can cost £100,000s.
Tasks workstations might be used for include:
CAD/CAM: Computer Aided Design and Computer Aided Manufacturing have been growth industries since the mid-1980s. These technologies allow engineers to design complex machine parts without having to produce an actual physical model. The necessary complex, 3-D graphics require a lot of computing power and good quality video capabilities.
Animation: Similarly to CAD/CAM, animations require a lot of processing power which must be performed quickly, and are ideally suited to the RISC technology.
Simulations: Performing simulations of processes, such as the behaviour of an industrial plant, requires considerable computing power.
Multitask programming: Any complex programming which is deemed to require more power than is offered by a PC, and which needs to perform more than one task at a time (called multitasking), is often performed on a workstation. Recent PC operating systems such as Windows NT can also perform multitasking.
The workstation will typically be part of a network.
Microcomputers are based on a microprocessor and are intended for individual use; hence they are called personal computers, or PCs. They were initially standalone machines, but are increasingly connected to a network. They are ideal for tasks such as those listed below where the user requires individual computing power.
Word processing: Word processing programs allow a user to produce professional-looking documents, with different fonts, styles and pictures. The production of complex and attractive documents is much easier with the use of word processing software than it was in the days of the typewriter.
Spreadsheets: Spreadsheets allow a user to create mathematical models. These are particularly useful in financial planning and can be used to answer questions such as ‘What happens if we raise the cost of our product by 1%?’.
Desktop publishing: This allows people to create drawings, manipulate images and combine them with text to produce professional graphic design work, for instance magazine layouts, posters, book covers, etc.
Games: Although this may seem a non-serious use of computers, games represent a large market. By making use of the PC's computing power very good quality graphics and complex game play can be achieved.
Servers: As mentioned above, many powerful PCs are now being used as servers to control a network.
Generally the tasks performed by the mainframes have been taken over by minicomputers. PCs initially created a new type of usage for the computer; for instance, spreadsheets and desktop publishing took over from activities previously performed by hand. As PCs have increased in power they have begun to be used for some of the tasks that required minicomputers and even mainframes in the past.
With the increase in computer power the distinction between types of computers is often difficult to maintain. When does a PC become a workstation for instance? Remember, though, that having an appreciation of the different types of computers and the tasks required of them is important, but you should not get too bogged down in trying to categorize machines.
This is the end of the background material. You should now do the exercise on practising note taking: Exercise - Note taking
In this exercise you will work individually to develop note-taking skills using a web type format.
The exercise should help you with the following:
using an HTML editor;
thinking about the course material.
One of the most important skills you can learn is how to take good notes. Not only how to take them, but to get into the practice of taking them. You may be thinking ‘I know how to take notes, what do I need this advice for?’. My response to this is that it is not just in this course you will find it useful, but in the whole of your life. We are repeatedly told we live in an information age. We are bombarded by information in a variety of media. In order to make sense of this information you have to be able to recall it and sort it into a useful order. A piece of information does not exist in isolation, but is connected to many other pieces of information. The connections you make can often make the difference between information being useful or not. Research in psychology has shown that people make more sense of information and retain it better if they actively do something with it, as opposed to just passively receiving it. The very act of using the information in some way makes it more ‘meaningful’ to each of us - we make connections and we remember them. One of the best and easiest activities for doing this is to make notes.
7.4 The exercise
Read the resource Taking notes - this describes the process of taking notes, deciding what and when to write, and the features of your notes you need to bear in mind.
Start up your preferred HTML editor. If you are unsure about using an HTML editor, here is some advice you may find helpful: Choosing and using an HTML editor.
Read over the material in this section again, and use the list of topics in the Summary section as headings to make notes in your HTML editor.
Read your notes, and synthesize them as you see fit.
Save the file with a suitable file name, for example "m1s1_7.htm"
As you take more notes during the course, revisit previous notes and make hyperlinks between material when you think there is a connection.
You should read the summary section next: Background material - summary
In this section you have covered some of the basic principles of how a computer operates, and what its various components do. You have also met some of the terminology used in the industry. You should now be able to read the set text, ‘Accidental Empires’, without coming across terms you are not familiar with.
You might like to discuss the following in your Tutor Group conference, or in the Forum.
Any parts of the background material you found difficult
Any questions about computers which have interested you
Any pieces of computer jargon you've heard but aren't sure what they mean
Anything else of interest relevant to this section.
In this section you have covered:
What software and hardware are.
The different categories of software.
What binary is, and how it relates to denary.
How a computer uses bits to represent information.
What analogue and digital mean.
The main components of a computer and their functions.
The factors that affect the power of a computer.
The difference between mainframes, minis, workstations and PCs.
Computer terminology, such as RAM, ROM, CPU, bytes, kilobytes, data, instructions, I/O, motherboard, buses and words.
Have a go at the Quick Quiz to see how well you have understood the content of this section on Background Material. This quiz is scored automatically, and no-one sees your score except yourself.
You should also complete the self-diagnostic form now. This will give you a record of your level of confidence with the Background Material.
The issues and concepts discussed here are more fully explored in the Open University courses Computers and processors (T224) and Building blocks of software (M263). T224 focuses on the hardware elements of personal computers whereas M263 looks at the role of software.
This is the end of Section 1 - Background material. You should refer back to the study guide to see that you have done all the work associated with this section or go on to Section 2. This looks at the invention of the microprocessor, and the company which is commonly associated with it: Intel and the microprocessor