Form 1 Computer Notes PDF

FORM ONE NOTES INTRODUCTION TO COMPUTERS Chapter outline 1.1 Introduction. 1.2 Parts of a computer. 1.3 Classification of computers. 1.4 Development of computers. 1.5 Areas where computers are used. 1. 6 The computer laboratory. 1.7 Practical hands on skills....

FORM ONE NOTES INTRODUCTION TO COMPUTERS Chapter outline 1.1 Introduction. 1.2 Parts of a computer. 1.3 Classification of computers. 1.4 Development of computers. 1.5 Areas where computers are used. 1. 6 The computer laboratory. 1.7 Practical hands on skills. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ 1.1 Introduction In the past, people have used slow and unreliable methods to generate, send, receive and store information. However, today millions of people are using devices called computers to produce, share and store information. Before embarking on taking Computer Studies as a course, it will be necessary to ask the question: What is a computer? Definition of a computer A computer is an electronic device that accepts user input also referred to as data and transforms it under the influence of sets of special instructions called programs to produce the desired output referred to as information. Data can be defined as raw facts that do not have much meaning to the user and may include: numbers, letters and symbols. Information is the processed data that is meaningful to the user. The computer is said to be electronic because it utilizes small electrical signals to process information. Before 20th century, most information processing was done manually or by use of simple machines. Today, millions of people are using computers In offices and at home to produce and store useful information about all Aspects of business, scientific research, government activities and Personal details. Together with other telecommunication facilities, computers have also become the fastest and most reliable means of communication. The integration of computers and, telecommunication facilities for the purpose of communication is what is referred to as information and communication technology (lCT).Computers come in different sizes and designs but the most common is a computer referred to as a personal computer (PC). Personal computers are mostly used in offices, schools, business premises and at home. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ 1.2 Parts of a computer A computer is made up of a collection of different components that are interconnected together in order to function as a single entity. A computer is basically made up of a system unit and other devices convicted to the system unit called peripheral devices. Examples of peripheral devices include; the monitor, the keyboard and the mouse. The system unit This is the part that houses the brain of the computer called the central processing unit (CPU). The system unit also houses other devices called drives. Drives are used to store, record and read data. Figure 1.2 shows a tower style system unit. Peripheral devices Peripheral devices are connected to the system unit using special cables called data interface cables that carry data and information to and from the devices. The cables are attached to the system unit using connectors called ports.. Peripheral. Devices may be arranged as shown in Figure 1.1 with the monitor resting on top of the system unit. Sometimes, the system unit may be made to stand alone (tower style) as the one in Figure 1.2. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ The keyboard It is the most common device that enables the user to enter data and instructions in the computer by pressing its keys. The mouse It is a device that enables the user to issue instructions to the computer By controlling a special mouse pointer displayed on the screen. The monitor The computer monitor or simply the screen is a television like device used for displaying output. It is called a monitor because it enables the user to monitor or see what is going on in the computer. 1.3 Classification of computers Computers can be categorised according to: 1. Physical size and processing power. 2. Purpose. 3. Functionality. Classification according to physical size and processing power Computers can be classified into four main groups namely supercomputers, mainframe computers, minicomputers and microcomputers. Supercomputers They are the fastest, largest, most expensive and powerful computers available. They are able to perform many complex calculations in a fraction of a second. Because of their extreme weight, a supercomputer is kept in a special room. Due to their huge processing power supercomputers generate a lot of heat. Special cooling systems are therefore required. Sometimes the whole CPU is immersed in an aquarium like tank containing liquid For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ fluorocarbon to provide cooling. Supercomputers are mainly used for scientific research, which requires enormous calculations. Applications that justify use of supercomputers include aerodynamic design and simulation, petroleum research, defense and weapon analysis among others. Supercomputers are mainly found in developed countries such as in USA where they are used for advanced Scientific research such as nuclear physics. Figure 1.3 shows an example of supercomputer. Mainframe computers They are less powerful and less expensive than the supercomputers. While supercomputers may be described as giant computers, the mainframes are said to be big in size. They are used for processing data and performing complex mathematical calculations. They have a large storage capacity and can support a variety of peripherals. Mainframe computers handle all kinds of problems whether scientific or commercial. They are mostly found in government agencies, big organizations and companies such as banks, hospitals, airports etc. which Have large information processing needs. Figure 1.4 shows a picture of a mainframe computer. Minicomputers A minicomputer resembles the mainframe but is slightly smaller. Thus it is referred to as a small-scale mainframe computer. Although it supports fewer peripheral devices and is not as powerful and fast as the mainframe computer, it was developed as For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ a cheaper alternative to the mainframes for smaller organizations. They are used mainly in scientific laboratories, research institutions, engineering plants and places where processing automation is required. They are well adapted for functions such as accounting, word processing, database management and specific industry applications. Figure 1.5 shows a picture of a minicomputer. Microcomputer A microcomputer is the smallest, cheapest and relatively least powerful type of computer. It is called a microcomputer because; its CPU is called a microprocessor, which is very small compared to that of a mini, mainframe or supercomputers. Microcomputers are also called personal computers (PC) because they are designed to be used by one person at a time. Microcomputers are commonly used in training and learning institutions, small business enterprises, and communication centers among others. Today, the power of microcomputers has grown tremendously closing the gap that formerly existed and reserved for the minicomputers and the mainframes. Technological advancement has seen the development of smaller and smaller microcomputers. The following are the various types of microcomputers in operation today arranged in descending order according to size. 1. The desktop computer -Not portable. It is designed to be placed on Top of an office desk. 2. The laptop computer -Portable like a briefcase. It is designed to be used by placing it on the lap hence its name. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ 3. The palmtop e.g. personal digital assistant (PDA) - Small enough to fit in the pocket and can he held in the palm when being used. Classification according to purpose Computers can be classified according to the tasks they perform either as general or special purpose computers. General-purpose computers General-purpose computers have been designed to be able to perform a variety of tasks when loaded with appropriate programs. They are the most common types of computers in use today. Their flexibility enables them to be applied in a wide range of applications like document processing, performing calculations, accounting, data and information management among others. Special purpose computers Special purpose computers are designed to serve a specific purpose or to accomplish one particular task. Such computers can perform no other task except the one they were meant to do. This means that the set of instructions, which drive a special purpose computer, are limited in number at the time of manufacture. Examples of such computers include, robots used in a manufacturing industry production line, mobile phones for communication only and electronic calculators that carry out calculations only. Since special purpose computers are dedicated to a single task, they can perform the task quickly and very efficiently. Classification according to functionality Computers can be classified according to the type of data they can For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ process. Data can either be in discrete or continuous form. Discrete data which is also called digital data is one that can be represented as distinct values that do not have any transitional stages over time e.g. either 1 or O. Continuous data which is also called analog data can be represented as progressively changing values overtime. Computers can be classified as digital, analog or hybrid. Digital computers Digital computers process digital data only. Any data to be manipulated by a digital computer must first be converted to digital form. Most home appliances today are also digital in nature. For example to increase the volume of a digital television you simply press a button and it changes from 1 to 2, 3 If the same television is analog, it would have a knob that you can continuously turn round or slide in a slot to increase or decrease the volume. Analog computers This refers to computers that process data that is analog in nature. Analog computers solve problems by measuring the amount of change that occurs in quantities like speed, temperature and pressure. An analog machine is usually a special purpose device that is dedicated to a single task. Analog computers are used in manufacturing process control like monitoring and regulating furnace, temperatures, and pressures. They are also used in other applications like in weather stations to record and process physical quantities e.g. wind, cloud speed, temperature etc. Hybrid computers Hybrid computers are designed to process both analog and digital data. 1.4 Development of computers Before 1900, most data processing was done manually using simple tools like stones and sticks to count and keep records. Around 2000 years ago, Asian merchants came up with a special calculating tool called abacus that could be used to calculate large figures. Abacii, are still in use even today. An abacus is made up of a rectangular frame and a crossbar at the middle. It is fitted with For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ wires or strings running across from the frame to the crossbar as shown in Figure 1.8. , 1+5=6 Each bead has a value of 5 Crossbar Each bead has a value of 1 4+5=90+0=0 3+5=8 Fig. 1.8: Representing numbers using an abacus 8 How to represent a number using an abacus Each bead in the lower row represents unitary values while the upper ones represent fives. To represent a number, the bead is moved to the crossbar. Those beads away from the crossbar represent zeros. The abacus in Figure 1.8 represents the number 6 908 (six thousand nine hundred and eight). The first machine after the abacus that is usually regarded as the forerunner of modem computers was developed by an English mathematician called Charles Babbage and was named the analytical engine. After the death of Babbage in 1871 there was little improvement on his work until the 1930s. The first computer- like machine Mark 1 was designed by Professor Howard Aken of Horrard University in 1939. Mark 1 became operational in 1943. It weighed 5 tons and was 16 m long. Since then, rapid advancements in computing have been realized and can be categorised into five generations. First generation computers (1940s to 1958) These computers were very large in physical size and used thousands of electronic gadgets called vacuum tubes or thermionic valves. These types of computers consumed a lot of power hence they constantly For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ broke down due to the excessive heat generated. Examples of such computers are the electronic numeric integrator and calculator (ENIAC) and the electronic discrete variable automatic computer (ED VA C). Second generation computers (1958 -1964) Computers in this generation operated using tiny, solid-state electronic devices called transistors that were much smaller than the vacuum tubes. These computers produced less heat, were much faster, smaller in size and more reliable than those made with vacuum tubes. Examples of second-generation computers include IBM 1401 and 7070, UNIVAC 1107, ATLAS LEO Mark III and Honeywell 200. Third generation computers (1964 -1970) The third generation computers used electronic devices called integrated circuits (ICs) instead of transistors. An integrated circuit consists of thousands of small transistor circuits etched on a semiconductor called a silicon chip. The use of integrated circuit improved the processing speed and storage capacity of computers. Examples of third generation computers included smaller and less expensive minicomputers such as IBM 360 and ILL 19000 series. Fourth generation computers (1970 to present) 51 From 1970, further technological improvement was done on the silicon chip design by compressing more tiny circuits and transistors into even smaller space. This design produced what is called large scale integrated (LS1) and very large scale integrated (VLS1) circuits which were used in the innovation and technological development of the brain of the computer called the microprocessor. A microprocessor is a complete central processing unit (Processor) used in microcomputers. The result was development of very small computers with very high processing speed. The first microcomputer was called Apple 11 Other fourth generation computers included IBM 370 and 4300, Honeywell DPS-88 and Burroughs 7700. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Fifth generation computers In this generation falls today's computers that have very high processing power and speeds than their predecessors, and whose size is increasingly becoming smaller. These computers have special instruction sets that allow them to support complex programs that mimic human intelligence often referred to as artificial intelligence. A lot of research is being done to try and come up with a machine that can work without human intervention. One of the most successful developments in this field is the advent of computers that can help managers to make decisions and those that can offer critical expert services to users instead of relying on human professionals. Areas where computers are used Computers have many advantages over other types of office and business equipments that are used for data processing functions. Three of the advantages are: 1. Computers process data faster. The processing speed of a computer measured against other devices like typewriters and calculators is far much higher. 2. Computers are more accurate. As long as the correct instructions and data are entered, computers W produce more accurate results. They have the ability to handle numbers up to many decimal places without rounding off. 3. Computers are more efficient. A computer utilizes minimum resources, to process data as compared to human beings or other machines. For example computers require less effort to process repetitive tasks. In our day to day activities, we use computers in almost every aspect of our lives. The following are some of the areas where computers are used. Supermarkets Most retail stores use computers to help in the management of daily activities like stock control. The stock control system keeps For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ account of what is in store, what is to be sold and what is out of stock. The management is automatically alerted when a particular item or items are running out of stock and need reordering. Offices Computers have increased efficiency in offices by reducing the time and effort needed to access and receive information. Most modern office functions have been automated for faster message distribution and document processing. Banks Special cash dispensing machines called automated teller machines (ATM s) have enabled automation of cash deposit and withdrawal services. Efficiency has also been increased due to better record keeping and document processing brought about by computers. Industries Computers are being used to monitor and control. Industrial processes. The computer age has seen the wide use of remote controlled devices called robots. A robot is machine that works like a human being but performs tasks that are too unpleasant, dangerous, or complex and tedious to assign to human beings. Hospitals Computers are used to keep patients records in order to provide easy access to a patient s treatment and diagnosis history. Computerized medical devices are now being used to get a cross sectional view of the Patient s body that enables physicians to get proper. Diagnosis of the affected part of the body with high levels of accuracy. Computers also control life support machines in intensive care units (lCU). Transport Computers are used to monitor vehicle traffic in a busy town, aircraft navigation and to make reservations. Communication For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Integration of computers and telecommunication facilities has made message transmission and reception to be very fast and efficient. Because of the speed with which information can be transmitted around in the world using computers the world is said to have become a global village. Law enforcement agencies Information held in computers such as fingerprints, photographs and other identification details helps law enforcers to carry out criminal investigations speedily. Education Computers are widely used in the teaching and learning process. Learning and teaching using computers is referred to as computer- aided learning (CAL) and computer aided teaching (CAT). For example experiments in subjects like Chemistry or Physics may be demonstrated using a special computer programs that can depict them on the screen through a process called simulation. Domestic and entertainment Computers can be used at home for recreational activities such as watching movies, playing music and computer games. They can also be used in storing personal information, calculating, keeping home budgets and for research in various fields. Library services In a computerized library, a computer enables library personnel to easily access and keep updated records of books and other library materials. Library users can also use computers to search for titles instead of using the manual card catalogue. 1.6 The computer laboratory A computer laboratory is a room that has been specially prepared to facilitate installation of computers and to provide a safe conducive environment for teaching and learning of computer studies. The following factors must be considered when preparing a computer laboratory. 1. Security of computers, programs and other resources. 2. Reliability of the source of power. 3. The number of computers to be installed and the available floor For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ space. 4. The maximum number of users that the laboratory can accommodate. Safety precautions and practices in the computer Laboratory After the establishment of the computer laboratory, a number of safety precautions, rules and practices need to be observed in order to avoid' accidental injury to the users, damage of computers or lack of a conducive environment for teaching and learning. The safety precautions and practices include: Behavior in the computer laboratory The following rules must be followed in and around a computer laboratory. 1. Avoid smoking or exposing computers to dust. This is because smoke and dust contain small abrasive particles that can damage computer components and cause wearing of moving parts. 2. Avoid carrying food and beverages to the computer room. Food may fall into the moving parts of the computer and damage them. Liquids may spill into computer parts causing rusting or electrical defaults. 3. Avoid unnecessary movements because you may accidentally knock down peripheral devices. 4. At all times follow the correct procedure for starting and shutting down the computer to avoid loss of data and damage to computer Programs. 5. Do not open up the metallic covers of computers or peripheral devices without permission and particularly when the computers power is still on. Protection against fire A computer room should have gaseous fire extinguishers like those filled with carbon dioxide. Water based or powder extinguishers should be avoided because they can cause damage to computer components. Cables insulation For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ All power cables in the computer room must be properly insulated and laid away from busy pathways in the room. Lay them preferably along the wall in trunks. This avoids the danger of exposing the user to electric shock and power interruptions caused by stumbling on cables. Stable power supply Computers are delicate devices that require a stable source of power. Power from mains supply is not always stable and may sometimes experience power surges or under voltage sometimes referred to as brownout. To protect the computer from being damaged due to power instabilities, avoid connecting it directly to the mains supply. Instead, connect it to a special device called un- interruptible power supply (UPS) then connect the UPS to the mains as shown below The UPS charges when mains power is on and has power surge and. brownout protection capabilities. When the mains power goes off, it gives some sound alert (usually a beeping sound) to alert the user. The UPS performs two main functions namely:  1. It regulates power from an unstable power source to the required Clean stable voltage by eliminating surges and brownouts. 2. It temporarily provides power to the computer in case of a sudden power failure hence allowing the user to store his/her work and shut down the computer using the correct procedure To enable continuity of work even in the absence of mains power, organizations that give critical services like banks, schools and hospitals usually install a standby generator that automatically comes on in case of a power failure. Power from the generator must pass through a UPS before being fed to the computer because it is also not stable. NB: Generally speaking, devices that provide alternative source of power are usually referred to as power backups. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Burglar proofing To deter unauthorized access to the computer room, it is important to implement the following controls. 1. Fit strong metallic grills and locks on doors, windows and roof in Case the roofing is weak. 2. Do not welcome strangers into the computer room. 3. Consider installing security alarms at strategic access points that would alert the security personnel in case of a break in. Ventilation There must be good air circulation in the computer room to avoid suffocation and overheating. Remember that both computers and human beings emit heat energy into the environment. Proper ventilation enables the computer to cool and hence, avoids damage to electronic parts that can be caused By overheating. Proper ventilation can be ensured by: 1. Ensuring that the room has enough ventilation points like windows. 2. Installing an air-conditioning system. 3. Avoiding overcrowding of either machines or people in the room. Dust and dump control a computer laboratory should be located away from excessive dust. The room should also be fitted with special curtains that would reduce entry of dust particles. Computers must remain covered using dust covers when not in use. Humidity should be at an optimum of 50%. Humidity lower than this allows static electricity to build up and causes damage to sensitive electronic components. also high humidity of over 70% cause rusting of the metallic parts of the computer system. To prevent both high and low humidity place humidifiers in the room Lighting a well lit computer room prevents eyestrain that eventually leads to headaches, stress and fatigue. It is important to adjust the For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ brightness of the computer monitor until the eyes feel comfortable before using a computer to avoid damaging your eyes: fit radiation filter screens. Which are specially tinted to reduce the light that reaches the eye. Avoid using a flickering monitor because this can cause extreme eyestrain that can damage eyesight. Standard furniture The table on which a computer is placed must be strong and wide enough to bear the weight and accommodate all the peripheral devices. The chair for the user must be comfortable, and have a straight backrest for one to sit upright as illustrated below to avoid muscle pains and backaches caused by poor posture. The seat must be high enough relative to the table for comfortable use of the hands on the keyboard and the eyes must be the same level as the top of the screen when the user is seated Practical hands on skills Starting-up (Booting) a computer 1. make sure that all the components are properly connected. The computer must be connected to an active power source. 2. Switch on the monitor first, 3. Switch on the system unit When the power is on, the computer automatically goes through a process of self-test and preparation for use. This process is called booting. There are two types of booting namely: * cold booting * warm booting. Cold booting This happens when the computer, originally off, is switched on by pressing the power button of the system unit. The computer starts by checking all its components to determine whether they are functioning correctly and whether they are available for use. This process is called the power-on-self-test (POST). During this process, the monitor will display information showing the status of each device being tested. In case one of the devices is faulty or missing, this process will halt and a message For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ alerting the user is displayed on the screen. The special program that directs the POST process is called the basic input output system (BIOS). When the POST process is over, the computer displays a prompt message requesting one to start using it. Some computers have programs that require a person to identify them selves by providing a user name and a password (a secret word given to the user) before it can allow one to use them. The process of providing such information is called logging on and it is a security measure meant to deter unauthorized users from using the computer. Warm booting (restarting) This happens when the computer, originally on, is forced to restart by pressing the restart button on the system unit or by pressing a combination of keys on the keyboard. It is also possible to warm boot a computer by using the restart command found in a special program called an operating system. Shutting down a computer It is important that the user follows the correct procedure of shutting down the computer at all times. If the procedure is not followed then loss of data, damage of programs and computer components may occur. Procedure for shutting down a computer 1. Ensure that all the work has been properly stored. This process is called saving. 2. Close all programs that may be currently running. 3. If your computer is running on Microsoft Windows 98 or later versions then: (a) Click the start button on the screen. (b) Select the shut down command from the menu list. (c) In the computer prompt that appears, select shut down then press the enter key on the keyboard. (d) After a few seconds the message IT IS NOW SAVE TO TURN OFF THE COMPUTER For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ appears on the screen. Switch of the system unit then the monitor. NB: Some system units switch themselves off automatically when you do steps 3 (a), (b) and (c) above. Keyboard layout The keys on the keyboard can be categorized into five groups as shown in Figure 1.11. Alphanumeric keys Keys are labeled with alphabetic letters A-Z, numbers arranged in a line 1,2, ……..0 respectively and symbols like:?,], % etc. This group also includes the following keys: cap lock, enter tab. space bar and backspace. Caps lock key: Pressing this key let's the user type in upper case- letters,(capitals) To switch back to lower case letters simply press the same key again. Enter key (return key): Pressing this key forces the text cursor to move to the beginning of the next line. A cursor is a blinking underscore (-) or a vertical beam (I) that shows where, the next character to be typed will appear. The enter key is also used to instruct.the computer to execute a command that has been selected on the screen. Tab key: This key is used to move the text cursor at set intervals on the same line e.g. 10 mm, 20 mm etc. The space bar: This bar creates a space between words during typing. The backspace key: This key deletes characters from right to left on the same line. Function keys For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Function keys are usually located along the top of the keyboard. They are labeled FI, F2 up to FI2. They are used for tasks that occur frequently in various programs. For example pressing FI key in J most programs starts the HELP MENU. Cursor movement and editing keys Cursor movement keys are used to move the cursor on the screen. These keys are: Arrow keys: Pressing the right or left arrow key moves the cursor one character to right or left respectively. Pressing the upward or downward arrow key moves the text cursor one line up or down respectively. Page up and page down keys: Pressing page up key moves the cursor up one page in case the document has many pages. Pressing page down key moves the cursor down one page in case the document has many pages. Home and end keys: Pressing home key moves the cursor to the beginning of the current line. Pressing end key moves the cursor to the end of the current line. Editing keys are used to delete or insert characters in a document. These are: Insert key: This key helps the user to insert or replace a character at the cursor position. Delete (Del) key: This key deletes characters at the cursor position from left to right. Special PC operation keys These keys are rarely used singly but in combination with other keys to give special instructions to the computer. They include SHIFT, CTRL, ALT and ESC keys. Numeric keypad keys The numeric keypad consists of a set of numbers 0 to 9 and the arithmetic signs like + (addition), (minus), * (multiplication) and / (division). They are located on the right hand side of the keyboard. The keypad is meant to help the user to rapidly enter numeric data. The numbers on the numeric keypad can only be used when the, situated on the numeric keypad, is turned on. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Otherwise, they can be used as cursor movement and editing keys when num lock key is turned off. It is important to note that not all keyboards have the numeric keypad. For example portable computers may lack a separate numeric keypad due to size limitations. Practical keyboard skills TYPING RULES: 1. Sit upright with both feet firmly on the ground maintaining an alert Posture. 2. Place the material to be typed on your left in a position you can read Without strain. 3. Rest both hands on the keyboard with fingers resting on the home keys. These are keys on which fingers rest during typing in readiness to press other keys. The home keys for the left hand starting with the small finger are A, S, D, F with the thumb on spacebar while those of the right hand are the apostrophe (') semicolon (;), L, K with the thumb on the spacebar. 4. Start typing the text slowly at first, making sure you are using all the Ten fingers and that you press the key nearest to the home keys with the closest finger, e.g. to press Q, use the small finger on the left hand while to press J, use the index finger on the right hand. Mouse skills Mice (the plural of mouse) comes in various shapes, colors and designs. Today one can even get a mouse that uses wireless technology that is, it does not have a connection cable. Most mice have two buttons but some may have three. Figure 1.12 is an illustration of a mouse. Using the mouse When the mouse is made to slide on a flat surface, it controls a pointer on the screen, which is called a mouse pointer or a cursor. To make a selection, the pointer must be on the item that is to be selected. After selecting, the user can manipulate the item by pressing a mouse button For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ USING THE MOUSE: 1. Place the mouse on a flat smooth surface. 2. Gently hold the mouse with your right hand, using the thumb and the two right-most fingers. 3. The index finger should rest on the left button while the middle finger rests on the right button. NB: For left handed people, it is possible to change the mouse settings in order to comfortably hold it using the left hand. Terminologies associated with the use of a mouse Clicking: This means pressing and releasing the left mouse button once. A click often selects an object. Double clicking: This means pressing the left button twice in quick succession. Double clicking usually opens a file or starts a program Right clicking: Pressing the right hand side mouse button once displays a list of commands from which the user can make a selection. This list of commands is called a shortcut menu or context sensitive menu. It is called a context sensitive menu because the commands on it apply to the right clicked item. Drag and drop: This is whereby the user drags an item from one location on the screen to another. The procedure to accomplish this operation is as follows: 1. Point to the item you want to drag. 2. Press the left hand side mouse button and hold it down 3. Slide the mouse until the pointer reaches the desired position on the screen. 4. Finally release the mouse button and the item will be dropped in the new location. COMPUTER SYSTEMS Chapter outline 2.1 Introduction 2.2 Input devices 2.3 The central processing unit (CPU) For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ 2.4 Output devices 2.5 Secondary (auxiliary) storage devices and media 2.6 Power and interface cables 2.7 Basic computer setup and cabling 2.8 Computer software 2.9 Criteria for selecting a computer system Introduction In the previous chapter, you were introduced to some of the parts or devices that make up a computer. However, a computer system requires more than just a collection of devices. The term system can be defined as a collection of independent entities that collectively work together to achieve a desired goal. The systems approach to computing was borrowed from the social scientists who believe that all things can be viewed as being made up of small independent components(subsystems) that come together to form a bigger more complex system. For example, a school can be seen as a system with the students, teachers, accounts department and the administration as subsystems. The school system itself is a subsystem of the ministry of education! Therefore, the term computer system refers to a collection of entities that work together to process and manage information using computers. It is important to note that, systems exist whether computerized or manual. However, the computer is replacing many manual processes hence the need to study the idea of a computer system. For example, a document processing system in the secretary s office can be made more efficient by computerizing it. A computer system consists of three main components namely the hardware, the software and the computer user (liveware). All the physical components both mechanical and electronic that make up a computer system such as the monitor, the system unit, keyboard and mouse etc. are called hardware. Software is a set of computer programs that guides the computer in each and every activity that happens inside the computer during data processing operations. Human beings by themselves have the ability though limited, to process data and manage information. Computers have been For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ designed to help human beings to enhance the efficiency of processing and managing information. It is the human being who issues commands to a computer depending on his or her needs. The hardware elements of a computer are generally grouped into four major categories namely input devices, central processing unit, output devices and storage devices. Input devices 'Data may be entered into a computer using keying devices such as the keyboard, or using pointing devices such the mouse, or by devices that automatically capture data from the source referred to as data capture devices e.g. scanners and digital cameras, or by voice recognition devices such as microphones. The main purpose of input devices is to convert the human readable data into electronic or machine readable form. Input devices can be classified according to how they are used to enter data. This includes: 1. Keying devices such as the keyboard, keypad etc. 2. Pointing devices such as mouse, trackball etc. 3. Scanning and other data capture devices. 4. Speech recognition or voice input devices. 5. Touch screen, digitizer and digital cameras. Keying devices Keyboard and keypad These are the most common input devices. These devices enter data into a computer by typing. Apart from a few differences, a computer keyboard is similar to the typewriter keyboard. A keypad is a miniature (tiny) keyboard which is mostly used on small portable computers, calculators palm notes, mobile phones etc. Pointing devices These are the input devices that enter data or instructions by controlling a pointer on the screen. Apart from the mouse, the other pointing devices include the trackball, joystick and light pen. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Trackball A trackball works just like the mouse but instead of moving it on a flat surface, a ball fixed on its top is rolled using the index finger. As the ball rotates, it moves a pointer on the screen; one can then click its button to execute the selected command. Figure 2.1 shows a drawing of a trackball. The advantage of a trackball over the mouse is that it neither requires an extra space nor a flat surface for movement. Today some computers are coming with a track ball on top of a keyboard and a mouse. Joystick A joystick is an input device that looks like a car gear lever which can be moved sideways, upwards or downwards to control the position of the cursor. Just like the mouse, it has a button which is used for selecting an item. It is commonly used in playing video games. Light pen A light pen is a hand held pen-like device that has a light sensitive point. A light pen can make selections, place images, draw and indicate dimensions by simply touching the screen. A light pen does not emit light 'but instead, it reacts to the light emitted by the display using a photosensitive. detector at its base. Scanning devices These are devices that enter (capture) data into the computer directly. Scanners can be classified according to the technology they use to capture data. These are optical scanners and magnetic ink scanners. Optical scanners These types of scanners capture data using light. A special type of concentrated beam of light is passed over the object, image or text which needs to be entered into the computer. The scanner converts For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ the data into digital form and then passes it to the computer for processing. There are three types of optical scanners: Optical mark recognition (OMR) These types of scanners detect marks made on a piece of paper using a soft pen or pencil. The reader scans the marks with a special type of light called infrared light. Where there are no marks, a strong light is reflected than where one exists. These types of scanners are used in marking multiple choice questions, questionnaires, selecting numbers in lottery tickets etc. Optical bar recognition (OBR) Bar codes are lines of different thickness that hold item information such as, country of manufacture, name of the manufacturer, and item code. The type of scanner used to read these bars is called a wand or a laser scanner. The interpretation is based on the width of the bars rather than their location. Figure 2.3 shows bar codes. Optical character recognition (OCR) / image scanners This is the most sophisticated type of scanner that operates like the human eye. It not only scans characters but also can scan real objects, pictures and drawings.  The most common type of this scanner is the flatbed scanner, Using this scanner, one can scan text, a real object or a picture by placing it on a glass plate exactly the way photocopy machine works. The text or a picture scanned is displayed on the screen or saved so that one can edit or print it. Magnetic scanners These types of scanners capture data by using magnetic technology. The data being read can either be in form of special magnetic characters or a continuous magnetic strip. The following are some of the common examples of magnetic scanners. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Magnetic-ink character recognition (MICR) MICR was developed to help banks process cheques. MICR allows special devices to read magnetic characters written in a special format. An example of MICR device is a cheque reader that reads the cheque number, and sends the details to the computer to be used in updating the customer s account. Magnetic stripe recognition A magnetic stripe is a thin magnetic tape, often found at the back of a plastic card e.g. an automated teller machine card (ATM) and a credit card. An ATM card is used to get banking services without necessarily going to the counter, while a credit card allows the holder to get services in any centre where the card is acceptable. The amount spent is deducted from the holder's bank account. Speech recognition or voice input Voice recognition is a type of input method where a microphone is used to enter data in form of spoken words into the computer. This method is mostly suitable for the handicapped especially those with impaired hands. Although this is a fast and easier method, it has some disadvantages. It is complex to develop and it does not take care of speech related problem' such as accents, inflections and tone. This implies that the device must learn the unique speech of an individual. Touch screen, digitizers and digital cameras Touch Screen Touch screen input method utilises the technology of a touch sensitive screen. When the user touches the screen, the computer detects the position of the finger and responds accordingly. Touch screens are mostly used in public places like in banking halls, hotels, in airports (to provide guidance information) etc. Digitisers A digitiser or a graphic tablet is almost similar to a light pen but instead it has a graphic tablet on which the user writes on using a device similar to a pen, called a stylus. (Figure 2.6). As the stylus For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ moves on the tablet, it s drawing is directly reflected on the screen. Digitisers are mostly used for architectural and engineering designs. Digital cameras A digital camera stores its images in digital form. These images can then be streamed (entered) directly into a computer for editing or printing by connecting the camera to a computer using a special cable. As with the ordinary camera, there are two types of digitals cameras: One that can takes still images i.e. photographs and another that takes motion pictures (video). The central processing unit (CPU) The central processing unit (CPU) also known as the Processor is the most important component of the computer. It is actually regarded as the brain of the computer. This is so because all data processing and control operations are coordinated here. In microcomputers, the CPU is housed inside the system unit. It is mounted on a circuit board known as, the motherboard or the system board. The figure below shows the location where a processor called Cyrix is mounted on the motherboard. The CPU has three different functional units called arithmetic and logic unit, control unit and the main memory. Arithmetic and logic unit (ALU) The arithmetic and logic unit is a unit of central processing unit where all arithmetic and logical operations are carried out. The basic arithmetic operations includes; addition, subtraction, multiplication and division. Logic operations are based on the computer s capacity to compare two or more values. For example, it may compare whether a piece of data is greater than or less than, For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ equal to or not equal to etc. In order for the ALU to be able to process data, it has special temporary storage locations called registers, which holds the data just before processing. It also holds the results after processing. Control unit Control unit coordinates all processing activities in the CPU as well as input, storage and output operations. It determines which operation or instruction is to be executed next. To coordinate these activities, the control unit uses a system clock. The system clock sends electric signals as its means of communication, just like the way the traffic signals or a traffic officer does in a round about or junction to direct motorists and other road users. The number of pulses per second determines the speed of a microprocessor. The faster the clock pulses, the faster the CPU hence the faster the computer can process data. Main memory (primary storage or working storage) Main memory also known as primary storage provides storage location for data and instructions accessed by the control unit. Computer memory can be classified into read only memory (ROM) and random access memory (RAM). Read only memory (ROM) Read only memory is used to store programmed instructions and data permanently or semi permanently. Data and instructions stored in ROM are those required to remain unchanged for long periods of time e.g. booting instructions, special purpose computers and computerized fuel pumps instructions etc. Depending on permanence of the instructions or data written on it, there are four types of read only memory namely; Mask read only memory: Once the content is written on it by the manufacturer, it cannot be changed. Programmable read only memory (PROM): This allows the user to alter it only once after the content is written on it. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Erasable programmable read only memory (EPROM): This has a transparent quartz window through which its contents, can be erased by exposing it to ultra violet (UV) light, and then reprogrammed for another use. Electrically erasable programmable read only memory (EEPROM): This type of ROM can be erased and reprogrammed using electricity. An example of EEPROM is the memory that stores the basic input/output system (BIOS). Characteristics of read only memory (ROM) are; 1. One can only read its content but you cannot write on it unless it is a special type of ROM. 2. It is non-volatile i.e. its content is not lost when the computer is switched off 3. Stores permanent or semi permanent instructions from the manufacturer called firmware. It can store semi permanent instructions because some variations of ROM chips can be programmed according to the user s specification. Random access memory (RAM) This is the most common type of main memory. It is called random access memory (RAM) because; its content can be read directly regardless of the sequence in which it was stored. As opposed to ROM, the content in RAM is held temporarily and its content is lost once the computer is turned off Therefore, before switching off the computer, it is important that one stores (saves) his/her work in a device that offers relatively permanent storage facility. Characteristics of random access memory (RAM) are: 1. Data can be read (retrieved) and written (stored) in it. 2. RAM is a temporary (volatile) storage because its content disappears when the computer is switched off. 3. Its content is user defined i.e. the user dictates what is to be contained in the RAM. Types of RAM For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ There are two types of-RAM namely, static RAM (SRAM) and dynamic RAM (DRAM). Static RAM is very fast compared to dynamic RAM and holds its content as long as there is power. Dynamic RAM on the other hand can only hold its content for a short while even when power is all. To maintain the content of dynamic RAM, the memory chip is designed in a way that its content is refreshed (automatically rewritten) severally per second. Static RAM is more expensive. It is mostly used to make special types of memories. Special purpose memories Apart from ROM and RAM there are several types of special purpose memories found insijkde the CPU or in the input and output devices. These memories are vital because they increase the overall performance of data and instructions moving in and out of the CPU. These memories include buffers, registers and cache memory. Buffers This is a temporary holding place that may be part of the CPU or built in an input or output device. Because the CPU is very fast compared to the input or output devices, buffers provide temporary storage so that the CPU is set free to carry out other activities instead of waiting for all data to be entered or information to be output. For example since a printer cannot work at the speed of a CPU, the printer buffers temporarily holds the output to be printed hence freeing the CPU to perform other functions. Buffers can hold more than one piece of data at a time. Registers As opposed to buffers, registers hold one piece of data at a time and are inside the CPU. Examples of registers are: An accumulator: This temporarily holds the results of the last processing step of the ALU. Instruction register: This temporarily holds an instruction just before it is interpreted into a form that CPU can understand it. An address register: This temporarily holds next piece of data For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ waiting to be processed. Storage register: This temporarily holds a piece of data that is on its way to and from the CPU and the main memory. Cache Memory Most modem processors incorporate small high-speed type of SRAM called cache memory. The purpose of cache memory is to allow the processor to access data and instructions even faster than it would have taken to fetch it from the relatively slow DRAM. Memory capacities Memory and storage capacity is measured in special units called bytes. A byte is equivalent to a single character. Characters can be a number from 0 to 9, letters A to Z or a special symbo1. For example, a number like 2545 has four bytes while the words, My Home has seven bytes since, and the space between them has 1 byte. Memory quantities can be expressed in; 1. Kilobytes (kB): Approximately one thousand bytes.(1024) 2. Megabytes (MB): Approximately one million bytes. 3. Gigabytes (GB): Approximately one billion bytes. 4. Terabytes: Approximately one trillion bytes.  Overall functional organization of the CPU The arithmetic and logic unit, the control unit and the main memory use electrical pathways or links referred to as buses. There are three types of buses namely; Control bus: This is the pathway for all timing and controlling functions sent by the control unit to other parts of the system. Address bus: This is the pathway used to locate the storage position in memory where the next instruction data to be processed is to be found. Data bus: This is the pathway where the actual data transfer takes place. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Figure 2.8 is a summary of the overall organisation of the CPU and how it controls other computer components. Control unit Gives Instructions instructions to Instructions each device after interpreting program instructions Arithmetic and logic unit Calculates and compares data Data to Results of be processing processed Input Main Output data memory data  I Input Stores data and Output unit instructions to unit I be processed temporally. Data to Output to be be stored processed Secondary storage devices Stores data and instructions to be processed permanently. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Fig. 2.8 Functional organisation of the CPU Types of processors and their clock speeds Processors In 1971, a company called Intel that specialises in manufacturing central processing units managed to combine the arithmetic-logic unit and the control unit on a single tiny processor called microprocessor and called it Intel 4004. This microprocessor was used in electronic calculators. The first microprocessor to be used on microcomputers was called Intel 8086 developed in 1974. Since then, there has been a tremendous growth in microprocessor technology marked by great increase in processing capability and speed. Until 1989, Intel corporation enjoyed monopoly in the field of microprocessor technology with her famous Intel processors. Since then other players joined in and started manufacturing cheaper alternatives. These include: Advanced Micro Devices (AMD), Cyrix and Motorola companies Processor clock speed The speed at which a processor executes instructions is determined by its clock speed. System clock speed is measured in hertz’s. A hertz is a unit of frequency which measures the number of cycles per second in a signal. Quantities of the clock speed can be expressed in; 1. Kilohertz (kHz): Approximately one thousand hertz’s. 2. Megahertz (MHz): Approximately one million hertz’s. 3. Gigahertz (GHz): Approximately one billion hertz’s. There has been a tremendous growth in the processing capability and clock speed of microprocessors. From a speed lower than 4MHz, modem microcomputers can run at speeds higher 2GHz. Table 2.1 shows a summary of how microprocessors have evolved. Processor Description Clock speed For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Intel The two are almost identical and were 4.7 MHz-I0 8086 used and 8088 with the first IBMPCs 8086 was an MHz improvement of 8088. Intel Provided increased performance over 6 MHz-20 80286 8086. This was the processor that opened up the MHz PCs to many users. 80386SX Apart from Intel s 80286, AMD produced 33 MHz-40 their versions with copied greatly the and MHz Intel s. These were the first entry in the processor 80368DX market. Provided over 100% better performance 80486SX 25 MHz-50 than and 80386 and were the first upgradeable MHz processors. AMD and Cyrix produced 80486DX their version too. Since 1992, Intel decided to coin their Pentiums 60 MHz- fifth generation with the name Pentium instead (586) and presently of above 80586. Pent is a Latin word that means Pentium IV  five. Intel chose the word in order to with over 2.8 distinguish its 80586 and above processors from AMD GHz and Cyrix versions i.e. 5x86 and AMDK5 respectively. Examples of Intel Pentium processor are Pentium Pro, Pentium MMX, Pentium II and currently Pentium IV at the time of writing this book. Output devices For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Output devices are peripheral devices that a computer uses to give out information produced after the processing operations. There are two types of output devices namely the softcopy and the hardcopy output devices. Softcopy refers to the intangible output mainly displayed on the screen or through other output devices such as speakers. A hardcopy is a tangible output produced mostly on papers by devices such as printers. Softcopy output devices. Some of the softcopy output devices are; Monitors A monitor or a video display unit (VDU) is the most common output device. It displays information on its screen thus helping the user to monitor operations carried out by the computer. For a long time, monitors have been designed using a long tube called the cathode ray tube (CRT at emits light. The screen of a cathode ray tube is curved slightly outward forming a convex shape. However, new flat displays have come which do not use CRT technology. Flat display are more comfortable to use, portable and do not consume a lot of power compared to CRT. Figure 2.9 shows a CRT monitor and flat panel display monitor. The sharpness or clarity of an image on the screen depends on the type of monitor being used. Monitors that display sharp clear images are said to have high resolution. The images on the screen are formed by small dots called picture elements (pixels). The higher the number of pixels per square centimeter the higher the resolution hence the clarity. There are two types of monitors namely monochrome and colour monitors Monochrome monitors display images and text in only one colour mostly black and white. Colour monitors can display images and text in multiple colours. For a monitor to display information it must be For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ connected to a separate piece of circuit board, plugged into the motherboard called the video card or graphics adapter. However, some motherboards have onboard video capability therefore there is no need for a video card. Examples of graphic adapters are: Monochrome display adapter (MDA): This was the first video card that was used in early computers. MDA displayed text only in one colour. Hercules graphics card (HGC): One weakness of the original MDA display was that, it could not support images of any kind. Hercule graphic card supports monochrome images in addition to text. Color graphics adapter (CGA): This can display text and images using up to 16 colours. Enhanced graphics adapter (EGA): This is an improvement over colour graphic adapter but also displayed text and images using 16 colours. Video graphics array (VGA): This offers at most 256 colours. Super video graphics array (SVGA): This is an enhancement of video graphic array capabilities offering over 256 colours. Small portable laptops, notebooks and even desktop PCs use flat-panel display. Common types of this display are: Liquid crystal display (LCD): Liquid crystal displays do not display by emitting light of their own. Instead they have tiny liquid crystals that reflect light falling on them from the environment. Liquid crystal displays are widely used in watches, calculators, cell phones and digital cameras. Electro luminescent (EL): These displays are an improvement on LCDs. Electro luminescent emits light when electrically charged. This makes them clear, sharper and easier to read. Gas-plasma: These use a gas that emits light in the presence of electric current. Thin film transistor (TFT): This is the latest technological advancement in displays. It provides high quality output than all the others. Sound output Speakers are used to output sound from a computer. Sound may be in For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ form of music, warning, video, interactive communication with a computer etc. Light-emitting diodes (LED) These are light emitting components that display light when an electric current is passed through them. A good example is the red or green light displayed by the system unit to help the user know whether it is on or off. Mostly LEDs are used to give warnings the same way a motorist would use signals to indicate when he/she is overtaking or taking a turn. LCD projectors project the output from the computer to a white board or wall. Hardcopy output devices The most common hard copy output devices are printers and plotters. Printers Printers produce a hard copy of information on papers. The quality of the hardcopy depends the printer s printing mechanism. There are two types of printers namely impact and non-impact printers. Impact printers The mechanism of impact printers is almost similar to that of an ordinary typewriter i.e. they produce characters by using special light hammers with characters or pins held on the printing head. To print, a paper is placed behind an ink ribbon. When the hammer strikes on the head, character mark is stamped. These printers are noisy and are mostly used to produce rough copies. The two widely used impact printers are dot matrix and daisy-wheel printers. Dot matrix printers produce a hardcopy by arranging patterns of dots on the paper using pins held in the printing head. Figure 2.10 (a) shows an example of an impact printer. Figure 2.10 (b) shows print characters formed by a dot matrix printer. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ a daisy-wheel printer has a wheel with petals on which characters are mounted. It is so called because it resembles a daisy flower. When printing, the wheel rotates allowing the petals to hit a ribbon with different characters as they are received from the computer. Non-impact printers These printers do not use the striking mechanism to produce characters on a piece of paper. They do not hammer the ribbon hence they are much quieter. The major non-impact printers are inkjet, thermal transfer and laser printers. Inkjet printers Inkjet printers form characters by spraying ink from tiny nozzles through an electrical field that arranges the charged ink particles into characters. Inkjets are cheap to buy but expensive to run because of the high cost of ink cartridges. Figure 2.12 shows an inkjet printer. Thermal printers Thermal printers use heat to transfer characters onto a piece of paper i.e. they bond characters onto a piece of paper by using hot pins which presses against a special ribbon. They are inexpensive alternative to inkjets. Laser printers Laser printers prints by passing a laser beam back and forth over a rotating drum. The laser beam draws the image on the drum by static electricity. An example of a laser printer is shown in Figure 2.13. The charged areas pick up the ink toner from a cartridge, and press it onto the paper. Although these printers are more expensive to buy, they are faster, and cheaper to run than the inkjets. Plotters A as shown in Figure 2.14, a plotter resembles a printer but specialises in producing big charts such as maps, pictures and drawings. They are mostly used for printing geographical, architectural and engineering drawings e.g. maps, advertisement posters to be placed on billboards, machine parts etc. 2.5. Secondary (auxiliary) storage devices and media For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ There is need to have an alternative long-term storage location for data and information other than the main memory. These alternative storage devices that are not part of the main memory are called secondary or auxiliary storage devices. These devices are not directly accessible by the cpu. Secondary storage devices that are not housed inside the system unit and hence can be carried around to be used with another computer are called removable storage devices and media. In order to read or store data from a storage media, a device called a drive is required. Secondary storage devices can be classified according to the technology used to record data. The technology could be magnetic or optical. The data and instructions held in these devices must first be moved into RAM before processing. Removable storage devices Magnetic tapes A magnetic tape is a ribbon of Mylar (plastic-like) material coated with a thin layer of iron oxide. The tape resembles the music cassette used in home tape recorders. In order to read/write data records on the tape, the tape must be inserted in a tape drive that rotates the tape allowing a read/write head to perform 5.1. the operation. Most computers today don t has tape drives because of the advent of better storage devices. Examples of magnetic tapes include: reel to reel tapes, cassette tapes and cartridge tapes. Disadvantages of using magnetic tapes 1. Magnetic tapes are slow because of the linear storage of data records on the tape. This means that you have to access the proceeding records before you get the required. 2. There is a space between successive data records called inter-record gap (IRG), which results in wastage of storage space. Magnetic disks They have a magnetic disk platter that stores data. Examples of magnetic disks are floppy disks (diskettes), zip disks and jaz disk. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Floppy disks " A floppy disk or simply a diskette is made up of a small flexible round disk coated with iron oxide. This disk is covered with a plastic protective case. Floppy disks are portable thus making them the most widely used type of secondary storage device. Floppy disks are inserted in a floppy drive, which has a read-write head that runs over the magnetised spots that contain data. Floppy disks come in different sizes with different storage capacities. Initial floppy disks were large in size but with smaller storage capacities than the presently available 3t-inch which has a maximum storage capacity of about 1.44MB. Figures. 2.15 (a) shows a typical 3t-floppy diskette while Figure 2.15 (b) shows parts of floppy disk. The structure of a floppy disk platter If the protective plastic casing of a floppy disk is removed, a circular flexible disk, coated with magnetic material will be revealed. The surface of the disk is divided into tiny invisible concentric circles called tracks that store data. The tracks are further divided into units called sectors as shown in Figure 2.16. Zip disks These are high capacity disks that resemble the floppy disks. They are, however, slightly larger and thicker in size. A zip disk can hold as much as 250 MB. Zip disks mostly come with separate-portable external zip drive. Jaz disks These are small portable disks with high storage capacity of about 1 GB to 2GB. They are used for storing data that require large storage. Like jaz disk comes with a portable jaz drive. Figure 2.17 below shows jaz and zip disks and their drives. Care of magnetic storage media To care for magnetic media the following rules are to be observed. 1. Do not expose them to strong magnetic fields. This would erase the magnetically recorded data on the disk. Hence do not carry magnets to the For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ computer room. 2. Keep magnetic media away from excessive heat because heat energy weakens magnetic media s ability to store data. 3. Do not drop the disk on the ground. Optical (laser) disks These are disks on which data is recorded using a laser beam. A laser beam is a very strong concentrated light. The beam bums very tiny holes (pits) into a thin shiny surface to record data. Likewise a laser beam in the optical drive is also used to read, record data on the disk. The advantages of optical storage media are: 1. They store very large volumes of data. 2. Data stored in them is more stable and more permanent than the magnetic media. Examples of optical storage disks include: LS-120 super disks (SD), compact disks (CDs), digital versatile disks (DVD), optical card and - optical tape. LS-120 super disk This is a diskette that resembles the 3 ½-inch floppy disk but uses optical technology instead of magnetic technology to record data. It has greater capacity of storage and greater speed of data retrieval. The LS-120 drive can read and write both the 3 ½-inch, 1.44 MB floppy disk and the 120MB super disk. (Figure 2.18). Fig. 2.18 Super disk and drive Compact disks (CD) Compact disks hold large quantities of data and information. One disk can hold as much as 700MB. They are mostly used to store data and information that requires a lot of space such as video clips, software, sounds etc. Figure 2.19 shows a compact disk. Currently compact disks are available in three forms namely: Compact disk-read only memory (CD-ROM): These are the type of compact disks which, when data is recorded on Them, one can neither change them, nor add anything on them. They are mostly used to store For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ music recordings. Compact disk-recordable (CD-R): These compact disks are initially blank but with a drive called CD- Writer, the user can record data, programs or information on it. However, once data has been written on it, one can only read but not change it. Compact disk-rewritable (CD-RW): Unlike the CD-Rs, these types of compact disks allows the user to record, erase and rewrite new information just as one would with floppy disks. NB: Both CD-ROMs and CD-Rs are referred to as WORM (Write Once Read Many) because they allow the user to record data on them once but read the data as often as necessary. Digital versatile disks (DVD's) Digital versatile disks also known as digital video disks resemble compact disks in every aspect but the only difference is that they have higher storage capacity of up to 17GB which is equivalent to approximately twenty six 640MB CDs. They are suitable for recording motion pictures such as video because they offer better sound and picture quality than the CDs. Optical card An optical card resembles the magnetic-ink character recognition card but instead of having a magnetic stripe, it has an optically recordable stripe that stores information. These types of cards are mostly used in banking and other business organisations to record customer details. Optical tape This is similar to a magnetic tape only that data is stored on it by using optical technology. Current and emerging trends in laser technology The advances in optical storage, digital video clips, voice and sound synthesis have formed the basis for modem multimedia technology exploited to develop multimedia computers. A multimedia computer does not only display text but can also allow the user to have sound playback For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ and watch videos and pictures. A typical multimedia computer must have the following minimum requirements: 1. A video graphic array or higher super video graphic array (SVGA) graphics card and monitor. 2. A sound card. 3. Compact disk or digital video disk drives. 4. 32 MB RAM or higher. Lower memory is bottleneck to performance. Today computers can be used to tune to any of the favorite FM or TV channels as long as an FM/TV card is installed in the computer. Fixed storage media These are the storage devices that are housed inside the personal computer s system unit. An example is the hard disk. However it is important to note that some hard disks especially those used in small computers such as laptops are removable. The hard disk The hard disk, also known as the Winchester disk is a sealed unit in which is shiny, rigid magnetic disks or platters that are arranged vertically on a  common axis as shown in Figure 2.20. How the hard disk stores data Each disk has two read/write heads that read/record data on both sides. The surfaces of each disk are divided into tracks and sectors like those of a floppy disk. Tracks along the common axis forms an imaginary cylinder. Therefore the term cylinder is sometimes used to indicate the For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ number of tracks on one surface of a platter. For example if you say that a hard disk has ten cylinders then each disk has ten tracks on one surface. If the disk has ten platters then one cylinder will have twenty tracks: As the disk rotates, the read/write head moves in and out over the surface to record or read data. Hard disks have gained widespread popularity because: 1. They provide permanent, cheap and large storage capacity that is rewritable. For example a computer can have one hard disk of 40 GB storage space. 2. They are very fast compared to other secondary s rage devices in terms of data transfer. Care of the hard disk Because of the high rotational speed of the disks, it is important to observe the following precautions to avoid permanent destruction to the hard disk also called disk crash. 1. Keep the disk away from smoke and dust. Dust and smoke particles can cause damage to the surface of the disk by scratching it as the head attempts to read data. 2. Switch off the computer using the correct procedure. This allows the read/write head to move off the disk surface before power is switched off. Improper procedure would risk heads crashing on rotating disks hence scratching them. Emerging trends in storage devices Because of need for vast storage prompted by today s massive data processing applications and need to carry a lot of information in easily portable storage devices, more advanced and reliable storage media are emerging. One good example is a storage device called the flash disk that is small in size (about 5 x 2 cm) but has capacity to store over 600MB ( equivalent to approximately 400 floppy For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ disks! !). Figure 2.22 shows a diagram of a flash disk. 2.6 Power and interface cables Power cables Inside the system unit is a special power supply unit that supplies power to the motherboard and other internal devices. In order to connect the computer to the mains power outlet, you need power cables that link the power supply unit to the outlet. Interface cables All peripheral devices are connected to the motherboard hence to the CPU by special cables called interface cables. An interface cable is connected to the device on one end, and to the motherboard via ports on the other end. The difference between the power cables and the interface cables is that the power cable supplies power to a component while interface cables transmit data signals. There are different types of cables and parts namely; Parallel cables and ports Parallel cables transmit information simultaneously using a set of many conductors (wires). For example if a cable uses 8 conductors to transmit data at the same time, it is said to be an 8-bit parallel cable. The advantage of using such cables is that they transmit data faster over a short distance. These cables are mostly used to connect printers and removable storage drives like the zip drive. Figure 2.23 shows an illustration For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ of a parallel port and cable. Serial cables and ports Unlike the parallel cables, serial cables transmit one bit at a time. Although they are slow, they are much more reliable than the parallel ports and therefore, their connector cables can be as long as 15 m. Serial cables are generally used to connect devices such as the mouse and some serial printers. Figure 2.24 shows a 9 and a 25 pin serial ports. Universal serial bus (USS) cable and port Universal serial bus is a new standard serial interface that is set to replace the conventional parallel and serial cables and ports. Currently most peripheral devices are coming with universal serial bus ports and interface cable. Although it transmits only I-bit at a time, it provides very high-speed and quality data transmission over distances of approximately 5 metres. USB supports a wide range of peripheral devices ranging from external storage drives to digital cameras. Figure 2.25 shows a USB port and its interface cable. If a computer does not have a universal serial bus port, it can be bought and fitted on the motherboard. Small computer systems interface (SCSI) cables and port This port and interface cables transmit data in parallel but are For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ faster than the parallel cables. Another advantage of the SCSI port is that one SCSI port allows us to connect up to eight peripheral devices. Other ports and connectors. Other ports and connectors include; 5-pin DIN and 6-pin (PS/2) ports Originally, most computers used the 5-pin DIN to connect a keyboard to the system unit but the smaller 6-pin mini-DIN also known as PS/2 interface port has almost replaced this technology. Currently most computers come with the PS/2 connector as the new standard to connect PS/2 mouse and keyboard. Figure 2.26 shows a 5-pin and PS/2 connectors showing physical difference in size. I Monitor ports The two most common connectors used for monitors are the 9- Pin D and the I5-pin Hi-D connector as shown in Figure 2.27. They are called D-ports because they resemble letter D. (Audio connectors These are jack plugs found on a sound interface adapter used to connect speakers, microphone and other portable audio equipment. 2.7` Basic computer For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ setup and cabling Having learnt about various devices and how they function, it is important to familiarise ourselves on how to setup a computer. Before attempting to carry out any setup activity, observe the following precautions should be observed. 1. Disconnect all devices from power source before starting to work on them. 2. Do not work on any peripheral device without the guidance of the teacher. 3. Never work alone because you may need help in case of an emergency. 4. Discharge any static electricity that might have built up on the hands by touching an earthed metallic object and then wearing an anti-static wrist member. This is because your body can hold as much as 200 volts of static charge that can damage sensitive components on the motherboard. Tools and other requirements The tools and requirements include; 1. Different sizes and shapes of screwdrivers. 2. Anti-static wrist member. 3. Pliers with narrow nose. 4. Manufacturer s manuals for motherboard and other components. 5. Necessary software. 6. A dismantled system unit. 7. Peripheral devices. 8. Interface and power cables. 9. Any other as needed. Connecting devices to the motherboard The following are For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ steps for connecting devices to the motherboard. Step 1: Identifying motherboard slots and components. Before you connect any device to the motherboard, carefully study the manufacturer s manual in order to identify the components labeled in Step 2: Connecting the hard disk, floppy drive and optical drive. These devices are connected to the motherboard using special ribbon cables like the one shown in Figure 2.30. The following instructions should be observed while connecting the devices:  1. Wear antistatic wrist member to discharge any static charge on the body. 2. Check that a free drive bay exists to hold the disk drive. 3. Slide the disk into its bay and screw it into place. 4. Ensure that there is a free power connector from the power supply unit and connect it to the drive. Notice that it is designed to fit in its socket in only one direction. 5. Identify pin 1 as labeled on the drives socket and match it with the red or brown continuous line of the ribbon cable. Most cables will only fit in one direction. 6. Connect the cable both to the drive then to the motherboard. 7. Repeat this for all the drives. 8. If installation is complete replace the system unit cover. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Step 3: Connecting other peripheral devices To connect a device to the system unit, you need to identify its port and interface cable. 1. Gently and carefully connect the interface cable of each device to the correct port and to the device if it is not already fixed permanently. 2. Connect the computer to the power source and switch it on. 3. Observe boot up information on the screen to see whether power on-self test (POST) displays any error message. 4. A successful boot means that the computer was properly setup. NB: If the computer is completely new, programs have to be copied (installed) on the hard disk. 2.8 Computer software As mentioned earlier, the term software refers to a set of computer programs. Its function is to guide the computer in its operations. Software can be classified according to purpose or acquisition. Classification according to purpose: Computer software may primarily be designed to manage the hardware resources or to help the user accomplish specific tasks. Therefore software may be classified as either system or application software. System software System software performs a variety of fundamental operations that avails computer resources to the user. These functions include: 1. Booting the computer and making sure that all the hardware elements are working properly. 2. Performing operations such as retrieving, loading, executing and storing application programs. 3. Storing and retrieving files. 4. Performing a variety of system utility functions. System software is further divided into: 1. Operating system. 2. Firmware. 3. Utility software. 4. Networking software. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ The operating system This is a set of complex programs that work together to control execution of user programs called applications and acts as a go between (interfaces) between the applications of the computer hardware. It manages input/output and storage operations in a computer. Examples of common operating systems are Microsoft Windows 95/98/2000/XP, UNIX, Linux, Macintosh (Mac OS) and OS/2. What type of operating system software do you use in the computer laboratory? Therefore the operating system is the main program on the computer system. Firmware Firmware, also referred to as stored logic is a combination of both the software and hardware recorded permanently on electronic chips. Usually, a firmware is a read-only memory chip that is mounted or plugged into the motherboard. Firmware may hold an operating system, utility programs, language processors etc. Utility software Utility software is a special program that performs commonly used services that make certain aspects of computing to go on more  smoothly. Such services include sorting, copying, file handling, disk management etc. The two basic types of utility software are: 1. System-level utility software: These help the user to work with the operating system and its functions. For example, a utility software tells the user when he/she enters a wrong command and gives suggestions how the error can be corrected. 2. Application utility software: These make the use of an application program smoother and efficient. These utility programs are commonly purchased separately or may be part of an operating system. Networking software This type of software is mostly used to establish communication between two or more computers by linking them using a For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ communication channel like cables to create a computer network. Networking software enables the exchange of data in a network as well as providing data security. Network software may come as independent software or integrated in an operating system. An example of networking software is novel Netware. Application software Application software, also called application packages are programs that are designed to help the user accomplish specific tasks..Table 2.2 gives examples and uses of common application packages Software Uses Examples Word Typing documents Ms Word, Lotus processor like letters. WordPro, WordStar. Spreadsheets Manipulation of Ms Excel, Lotus numeric data e.g. 1 2 3 calculating budgets. Desktop Designing Adobe publications PageMaker, Publisher like newspapers, Ms publisher. books. Computer Technical drawing. AutoCAD. aided Design Databases Keeping records Ms Access, and Dbase. files. Graphics Creating and Corel Draw,’ software Adobe manipulating Photoshop. pictures. Table 2.2: Application packages For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ Classification according to acquisition Generally computer programs can be classified according to how they are obtained as in-house developed software and standard software (Vendor off-the-shelf software). In-house developed programs These are programs that are uniquely designed and tailored to meet a particular user s needs. For example, a bank may decide to manage its banking operations using a unique program developed by hired programmers. These programs are not available in the shops and once developed for one company or user may not address the needs of other users. Standard software (Vendor off-the-shelf software) These programs are developed by software engineers, packaged and then made available for purchase through a vendor, a distributor or directly from the developer. A developer may bundle more than one but closely related software into one package to form a suite or integrated software as opposed to single-purpose software. Examples of suites are Lotus Suite, Microsoft-Office and Corel WordPerfect while those of single purpose are QuickBooks and Sage Line 50. The word package is sometimes used to refer to these types of software that are packaged and sold by vendors. Advantages of standard software over the in-house developed programs are: 1. They can easily be installed and run. 2. They are less expensive to acquire than the cost of developing in-house software. 3. They are readily available for almost any task. 4. Since they are thoroughly tested before they are released, chances of errors in them are rare. 5. They can easily be modified (customised) to meet specific user’s For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ needs without involving expert programmers Criteria for selecting a computer system The task of determining a suitable computer system for an individual or organisation is not easy. A good computer system must meet all the requirements of the user. Therefore, before selecting the computer system to implement, it is advisable to do an analysis of all the requirements necessary in order to avoid acquiring a system that may disappoint the users. Requirements analysis for selecting a computer system should cover the following: 1. Identifying all user requirements. 2. Evaluating hardware requirements that will meet the users needs. 3. Evaluating software requirements that will meet the users needs. The computer hardware and software to be acquired should therefore be able to meet all needs of the data processing environment that, they are intended for effectively. Hardware considerations Some factors considered when selecting computer hardware are; Processor speed The processing power and speed of a computer mainly depends on the processor speed. A good computer must have high processor speed. For example a few years ago, processors used to have speeds of less than 100 MHz. However, today s Pentium processors are operating at very high clock speeds of over 4 GHz. Scientists and engineers are aiming at producing a processor that operates at terahertz (trillion hertz). However, it is important to buy a processor that suits ones need not necessarily the fastest. Memory capacity As earlier mentioned, primary memory, mainly random access memory (RAM) is measured in megabytes (MB). For example, a computer may have 32MB of RAM. Although, a computer may have a very fast processor, it may not perform as expected if it has low memory capacity. Because of the current multimedia driven For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ applications, a good computer should have sufficient memory to handle the heavy applications that require a lot of memory space in order to run. A computer with at least 128 MB of RAM is recommended for most contemporary applications. RAM is packaged as either dual in-line memory Module. (DIMM) or single in-line memory module (SIMM). Therefore, before one buys a memory module for the computer the following factors have to be considered: 1. The type of module supported by the computer s motherboard. 2. Does the motherboard have an empty memory slot? 3. Will the module work well (be compatible) with the other existing modules on the motherboard? 4. What is the capacity of the module? Warranty A warranty is an agreement between the buyer and the seller that spells out terms and conditions of, after selling a product in case of failure or malfunction. The most important consideration to make is whether the seller is ready to actually provide after sales services. On top of the actual cost of the item, most manufacturers and suppliers include a certain percentage charge to cover the warranty.  A good warranty should cover the following points: 1. Scope of cover for example six months, one year etc. 2. Callout response and liability agreement. For example how long should the supplier take to repair a fault or replace the product, and if he/she delays who bears the cost. 3. Preventive maintenance for example regularity of service, at intervals etc. Cost The cost of a computer system depends on: 1. Its processing capability. 2. Whether it is branded or a clone. Branded computers are more expensive than their equivalent clones. This is because of their reliability and good after sale services. For free KCSE Notes, Exams, and Past Papers Visit https://Teacher.co.ke/ 3. Its size. Portable computers are more expensive than their desktop equivalents because of the superior technology involved in manufacturing smaller components without losing performance abilities. It is important to do a market survey from magazines, newspapers, and electronic media or visit a number of vendors to compare prices before purchasing a computer. Computer information and technology exhibitions also enlighten a buyer on current trends and costs. Upgradeability and compatibility When buying a computer, the best option would be to get one that can easily