FOC001_ Fundamentals of Computer

Classification of Computers 43 Processing Laptops are usually associated with Notebooks nowadays come in laptop Capacity higher processing power than configurations but the size factor wears notebooks. Normally 1-8 GB RAM. off as it becomes more powerful and the sense of notebook is gone. Physical A laptop usually weighs between 1.4 A notebook weighs less than 5 pounds characteristics to 5.4 kgs (3 to 12 pounds). and is 3 inches or less in thickness. Subnotebook Fig. 3.13: Subnotebook Computer A subnotebook is a class of laptop which are smaller and lighter than typical notebooks. It is also called ‘ultraportable’. They generally are found to run full desktop operating systems such as Windows or Linux, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS. Subnotebooks are smaller than laptops but larger than handheld computers. They often have smaller-sized screens, less than 14 inches and weigh less than typical laptops, usually being less than 2 kg (4.4 lbs). The savings in size and weight are usually achieved partly by omitting ports or having removable media or optical disc drives. Palmtop A palmtop is a hand-held microcomputer, i.e., small enough to be held in one’s hand. Although extremely convenient to carry, handheld computers have not replaced notebook computers because CU IDOL SELF LEARNING MATERIAL (SLM)

44 Computer Fundamentals of their small keyboards and screens. The most popular palmtop computers are specifically designed to provide PIM (Personal Information Manager) functions, like a calendar, address book, etc. Fig. 3.14: Palmtop Computer Personal Digital Assistants (PDA) A Personal Digital Assistant (PDA) is a hand-held microcomputer that trades off power for small size and greater portability. They are tightly integrated computers that often use flash memory instead of a hard drive for storage. These computers usually do not have keyboards but rely on touch-sensitive LCD screen for both output and input. PDAs communicate with desktop computers and with each other either by cable connection, infrared (IR) beam or radio waves. It can function as a cellular phone, fax sender and personal organizer. PDAs are normally used to keep track of appointment calendars, to-do lists, address books and for taking notes. Fig. 3.15: Personal Digital Assistant (PDA) CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 45 Pocket PC A Pocket PC is a hardware specification for a handheld-sized computer (PDA) that runs the Microsoft Windows Mobile operating system. It may have the capability to run an alternative operating system like NetBSD or Linux. Fig. 3.16: Pocket PC Pocket PCs can also be used with many other add-ons like GPS receivers, barcode readers, RFID readers and cameras. Tablet PC A Tablet PC is a notebook or slate-shaped mobile computer, first introduced by Pen computing in the early 90s with their PenGo Tablet Computer and popularized by Microsoft. Its touchscreen or graphics tablet/screen hybrid technology allows the user to operate the computer with a stylus or digital pen or a fingertip, instead of a keyboard or mouse. Tablet PCs are often used where normal notebooks are impractical or unwieldy or do not provide the needed functionality. Fig. 3.17: Tablet PC CU IDOL SELF LEARNING MATERIAL (SLM)

46 Computer Fundamentals Ultra-Mobile PC The Ultra-Mobile PC (UMPC) is a specification for a small form factor tablet PC. It was developed as a joint development exercise by Microsoft, Intel and Samsung, among others. Current UMPCs typically feature the Windows XP Tablet PC Edition 2005, Windows Vista Home Premium Edition or Linux operating system and low-voltage Intel Pentium or VIA C7-M processors in the 1 GHz range. Fig. 3.18: Ultra-Mobile PC Home Theater PC A Home Theater PC (HTPC) is a convergence device that combines the functions of a personal computer and a digital video recorder. It is connected to a television or a television-sized computer display and is often used as a digital photo, music, video player, TV receiver and digital video recorder. Fig. 3.19: Home Theater PC Home theater PCs are also referred to as media center systems or media servers. Because of the nature of the HTPC, higher than average capacities are required for HTPC units to allow storage of pictures, music, television shows, videos and other multimedia HTPC cases have a small LCD screen on the front where a user can view music/movie information. Workstation/Server Computer A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 47 network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected to a network. Historically, workstations had offered higher performance than personal computers, especially with respect to CPU and graphics, memory capacity and multitasking capability. They are optimized for the visualization and manipulation of different types of complex data such as 3D mechanical design, engineering simulation, animation and rendering of images, scientific calculations and mathematical plots. Workstation Computer Server Computer Fig. 3.20: Workstation/Server Computer The workstation class Personal Computer may have some of the following features: (i) Support for ECC (Error Correction Code, i.e., a system of error control for data transmission) memory. (ii) A larger number of memory sockets which use registered (buffered) modules. (iii) Multiple processors. (iv) Multiple displays. (v) Run a “business” or “professional” operating system version. Server usually refers to a computer that is dedicated to providing a service to other computers over a network. A server application is a computer program that accepts connections in order to service requests by sending back responses. Servers usually have powerful processors, lots of memory and large hard drives. Examples of server applications include web servers, e-mail servers, database servers and file servers. CU IDOL SELF LEARNING MATERIAL (SLM)

48 Computer Fundamentals Client-Server Computer Client–Server Computing or networking is a distributed application architecture that partitions tasks or work loads between service providers (servers) and service requesters (clients). Often clients and servers operate over a computer network on separate hardware. Classic client- server architecture requires one of the communication endpoints to act as a server, which is much harder to implement. A server machine is a high-performance host that is running one or more server programs which share its resources with clients. A client does not share any of its resources but requests a server’s content or service function. Clients therefore initiate communication sessions with servers which await (listen to) incoming requests. The most basic type of client-server architecture employs only two types of hosts – clients and servers. This type of architecture is sometimes referred to as two-tier. It allows devices to share files and resources. The two tier architecture means that the client acts as one tier and application in combination with server acts as another tier. Fig. 3.21: Client-Server Computer In most cases, a client-server architecture enables the roles and responsibilities of a computing system to be distributed among several independent computers that are known to each other only through a network. This creates an additional advantage to this architecture: greater ease of maintenance. CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 49 For example, it is possible to replace, repair, upgrade or even relocate a server while its clients remain both unaware and unaffected by that change. All data is stored on the servers, which generally have far greater security controls than most clients. As the number of simultaneous client requests to a given server increases, the server can become overloaded and this is the main disadvantage of client-server computer. Embedded Computers An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions often with real-time computing constraints. It is usually embedded as part of a complete device including hardware and mechanical parts. They generally execute a program that is stored in non-volatile memory and is only intended to operate a specific machine or device. Embedded computers are typically required to operate continuously without being reset or rebooted and once employed in their task the software usually cannot be modified. Embedded computers are very common. Embedded systems range from portable devices such as digital watches and MP4 players, to large stationary installations like traffic lights, factory controllers or the systems controlling nuclear power plants. Fig. 3.22: Embedded Computer Wearable Computer The latest trend in computer is Wearable Computer. A wearable computer is a computer that is subsumed into the personal space of the user, controlled by the user, and has both operational and interactional constancy, i.e., is always on and always accessible. They have been applied to areas CU IDOL SELF LEARNING MATERIAL (SLM)

50 Computer Fundamentals such as behavioral modeling, health monitoring systems, information technologies and media development. Wearable computers are especially useful for applications that require computational support while the user’s hands, voice, eyes or attention are actively engaged with the physical environment. One of the main features of a wearable computer is consistency. There is a constant interaction between the computer and user, i.e., there is no need to turn the device on or off. Another feature is the ability to multi-task. It is not necessary to stop what you are doing to use the device; it is augmented into all other actions. These devices can be incorporated by the user to act like a prosthetic. It can therefore be an extension of the user’s mind and/or body. 3.3 Applications of Computer (a) Banking: Banks uses computers for general purpose computations, to maintain ledger, to handle transactions, to make entry in passbooks, to issue fixed deposit receipts, to provide online service to customers who want to perform bank transactions from home terminals and to answer customers at bank terminals regarding their balance etc. For all these purpose there is a central computer (a server) which processes all the data from different terminal computers. These days banks also provide the ATM (Automatic Teller Machine) service to the customers. A customer with the ATM card can perform a cash transaction immediately with the ATM machine by inserting card in it. Fig. 3.23: Banking (b) Home-based workers: Now that it is easy to connect a computer at home to all of the computers at the office, more and more people are working at home. These telecomputers CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 51 often work one or more days without the traditional commute. The same ability to communicate so easily makes home-based business easier to start and operate. (c) Desktop publishing: Producing finished business literature is one of the uses of computer in business. Using desktop publishing programs, or even sophisticated word processing programs, people can create sales letters, brochures, price lists, newsletters, and even book-length manuals. (d) Financial analysis: Financial analysis is performed throughout the company, from top management to down. People can analyze investments, sales, expenses, markets and other aspects of the business using both numbers and graphs. Computer in Commercial Many business companies, large or small use computers to help in the control of daily activities. Some of the more common uses are: Fig. 3.24: Computer in Commercial (a) Employee records: All organizations keep record of their employees. An employee record normally contains information such as name, address, telephone number, present job classification, date of start of employment, contract period, salary scale or rate of pay, allowances, deductions, salary paid to date, taxes deducted to date, etc. Using a computer, it is a simple matter to store, retrieve and update information concerning employees. The most frequent use of an employee record is in payroll processing. CU IDOL SELF LEARNING MATERIAL (SLM)

52 Computer Fundamentals (b) Payroll processing: With the employee record we have almost every information of an employee. Regarding the payroll the fields such as employee name, address, job classification, rate of pay, fixed allowances, fixed deductions etc., are important. With different information such as number of hours worked by each employee, fixed allowances, fixed deductions etc., the gross pay is calculated. (c) Accounts receivable: An account receivable system keeps track of all money owed to the company by its customers. e.g., consider a department store which offers credit to selected customers. For each customer record is created which include date such as customer name, address, telephone number, occupation, credit limit, amount owed by the customer, date of last purchase, date of last payment, etc. The date of last purchase, date of last payment data items are used by the computer to determine the length of time for which the customer has owed money to the store. Based on this time a notice can be sent to the customer, if he/she is too late to pay. (d) Account payable: An accounts payable system keeps records of people to which the company owes money. These are usually the people who provide goods and services to the company. This system enables the company to schedule its payments in a way which is in the best interests of the company. (e) Stock control: A stock control system enables a user to mange his stock more effectively. At the heart of the system is the file of stock items. For each item in stock, an ‘item record’ is created. Each item is assigned a unique identifier (usually a number). This number is used in all transactions to do with the item. Computer in Industry Computers have had a major impact in industries where products are designed and manufactured. Computer Aided Design (CAD) is used to develop products. Computer Aided Manufacturing (CAM) is used to produce them. CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 53 Fig. 3.25: Computer in Industry (a) Product design: Designing complicated products can require the efforts of thousands of people working together. This teamwork is greatly enhanced through the use of computerized design. (b) Factories: Factory floors are becoming increasingly populated by computers used for many purposes including inventory control and planning and process control. Computers are also used to run robots that create, finish, assemble, and test products and their components. Computer in Health Care and Medical field Computers are widely used in hospitals to help doctors in diagnosis, getting information on patients, diseases, treatment, drugs etc. They are also used in administration and in keeping patient records. Doctors can get information from distant data banks and expert systems. They can discuss with colleagues using teleconferencing. Many devices take images and diagnose diseases. Examples are Computerized Axial Tomography (CAT), Position Emission Tomography (PET), Magnetic Resonance Imaging (MRI), etc. These devices take pictures of brain and help in diagnosis of various kinds of diseases. There are a lot of computerized automatic medical equipments which help in diagnosis of diseases such as CT scan machine, Eye testing machines, Ultra sonography equipment, etc. CU IDOL SELF LEARNING MATERIAL (SLM)

54 Computer Fundamentals Fig. 3.26: Computer in Health Care and Medical Field Computer in Education Computers have been used in schools since the first Apples were introduced in the 1970. However, their impact was limited then because there were not enough computers and educational computer programming was poor. As technology has advanced education, software has become a major influence at all levels from elementary schools to universities. The ability to connect computers and students together over a network such as the Internet opens up fantastic educational opportunities. Fig. 3.27: Computer in Education CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 55 (a) Research and Universities: Scientific and engineering design and research work involve complex and massive computations. In many cases, simulation is also required. Such complex computations are not possible by hand calculators. So, computers are must for this type of work. (b) Library: A typical library contains thousand of books, magazines, reports and other documents which users may wish to borrow. A small library may have several hundred prospective borrowers, while the number of users of larger libraries can reach beyond thousands. Maintaining records of books and borrowers is well suited to a computer system. Using a computer enables library personnel to answer queries about the status of books more easily than if a manual system was being used. A computerized system also enables to find out whether to issue books to the users or not. If the maximum limit of the book is already reached then that user will not get the book. Computer in Engineering Computer Applications in Engineering Education provides timely information on the innovative uses of computers and software tools in education, and for accelerating the integration of computers into the engineering curriculum. In modern times, computers have closely connection with everyone, especially scientist and engineer. Computer programs can now solve difficult problems in a fraction of the time it used to take. Computer-aided engineering is a powerful tool and necessary for engineering design and manufacture. Fig. 3.28: Computer in Engineering CU IDOL SELF LEARNING MATERIAL (SLM)

56 Computer Fundamentals Nowadays, you no longer have to write your own software programs to use computers effectively. In chemical engineering, a lot of softwares are used in the process of chemical operation, like the software for process of chemical engineering Proa! and Aspen, and Computational fluid dynamics software Fluent and CFX and so on. Computer in Graphics Today, computers and computer-generated images touch many aspects of daily life. Computer graphics is found on television, in newspapers, for example, in weather reports, or for example, in all kinds of medical investigation and surgical procedures. Fig. 3.29: Computer Graphics Cartoon The development of computer graphics, has made computers easier to interact with and better for understanding and interpreting many types of data. Computer imagery has applications for film special effects, simulation and training, games, medical imagery, flying logos, etc. Although computer graphics is a vast field that encompasses almost any graphical aspect, it mainly interested in the generation of images of three-dimensional scenes. CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 57 3.4 Basic Components of PC When you look at a computer closely, you can name the following main parts: Fig. 3.30: Parts of Computer Mouse A mouse is used to replace the key combinations with easier point and click actions. The mouse is connected to the main board of the computer by a cable. It is input device. Keyboard  It has many small keys on it.  The computer accepts data with the help of keyboard. Monitor This part looks like a TV screen with the help of this.  We can see what has been typed into the computer.  It displays the resulting output.  It is also called a Screen/VDU (Visual Display Unit). CU IDOL SELF LEARNING MATERIAL (SLM)

58 Computer Fundamentals Hard Disk Drive  The computer stores information permanently in it.  The hard disk is the fixed storage. CPU (Central Processing Unit)  It is housed in the main unit.  It is a small silicon chip.  It is the brain of the computer and does all the manipulation of data we give to the computer. CD-ROM Drives CD-ROM stands Compact Discs-Read Only Memory. CD-ROM drives reads programs and data stored on a removable CD drives. These drives can hold large amount of information. Floppy Disk Drive  The computer can store information in a floppy disk.  This is a removable storage. Printer It is a output device. We can see the resulting output on the monitor but to print it on paper we need a printer. 3.5 Computer Architecture A computer system is one that is able to take a set of inputs, process them and create a set of outputs. This is done by a combination of hardware and software. In describing Computer systems a distinction is often made between Computer Organization and Computer Architecture. Computer Architecture In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization and implementation of computer systems. Computer architecture is the CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 59 architectural attributes like physical address memory, CPU and how they should be made and made to coordinate with each other keeping the future demands and goals in mind. It is concerned with structure and behavior of computer as seen by the user. Computer Organization Computer Organization refers to the Operational Units and there interconnections that realize or recognize the specifications of Computer Architecture. Computer organization is how operational attributes are linked together and to realize the architectural specifications. So, from the definition, we can easily understand that Computer Architecture is: Set of Instructions + Computer Organization = Computer Architecture High level Application program Application design Software System design Computer architecture Computer design Computer Logic design Hardware Organisation Circuit design Computer Componment Low level Fig. 3.31: Computer Architecture The distinction between computer organization and computer architecture is often misunderstood. For example, if computer organization examines the lumber, bricks, nails and other building material, while computer architecture looks at the design of the house. CU IDOL SELF LEARNING MATERIAL (SLM)

60 Computer Fundamentals 3.6 Summary As personal computers, laptops are capable of the same tasks, although they are typically less powerful for the same price. They contain components that are similar to their desktop counterparts and perform the same functions, but are miniaturized and optimized for mobile use and efficient power consumption. Computers can be broadly classified by their speed and computing power. It is a multi-user computer system, capable of supporting hundreds of users simultaneously. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet CD-ROM stands for compact discs-read only memory. CD-ROM drives reads programs and data stored on a removable CD drives. These drives can hold large amount of information. The term ‘desktop’ refers specifically to a horizontally-oriented case, usually intended to have the display screen placed on top to save space on the desktop. Most desktop computer offer more power, storage, versatility and low cost. A laptop is a small mobile computer, which usually weighs 2.2-18 pounds (1.6 kilograms), depending on size, materials and other factors. A laptop is designed to sit on user lap and user can therefore expect it to be quite large and loaded down with features and power. A sub notebook is a class of laptop which are smaller and lighter than typical notebooks. It is also called ‘ultraportable’. They generally are found to run full desktop operating systems such as Windows or Linux, rather than specialized software such as Windows CE, Palm OS or Internet Tablet OS. A Personal Digital Assistant (PDA) is a hand-held microcomputer that trades off power for small size and greater portability. They are tightly integrated computers that often use flash memory instead of a hard drive for storage. CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 61 3.7 Key Words/Abbreviations  Analog Computer: Analog computers are computers that measure physical quantities.  Digital Computer: Digital computers are counting digital devices.  Hybrid Computer: The features of analog and digital machines are combined to create a hybrid computing system.  Desktop: Most desktop computer offer more power, storage, versatility and low cost.  Laptop: A laptop is designed to sit on user lap and user can therefore expect it to be quite large.  Personal Digital Assistants (PDA): PDAs communicate with desktop computers. 3.8 Learning Activity 1. What is computer architecture? Explain the applications and basic components of computer. —————————————————————————————————— —————————————————————————————————— 2. Explain different types of computer with their merits and demerits. —————————————————————————————————— —————————————————————————————————— 3. Explain different generation of computer and their development. —————————————————————————————————— —————————————————————————————————— CU IDOL SELF LEARNING MATERIAL (SLM)

62 Computer Fundamentals 3.9 Unit End Questions (MCQs and Descriptive) A. Descriptive Type Questions 1. What is Computer Organization? 2. Explain the types of Computer. 3. Differentiate between Laptop and Notebook. B. Multiple Choice/Objective Type Questions 1. UNIVAC is __________. (a) Universal Automatic Computer (b) Universal Array Computer (c) Unique Automatic Computer (d) Unvalued Automatic Computer 2. CD-ROM stands for __________. (a) Compactable Read Only Memory (b) Compact Data Read Only Memory (c) Compactable Disk Read Only Memory (d) Compact Disk Read Only Memory 3. Which of the following is called low level languages? (a) Machine language (b) Assembly language (c) Both [a] and [b] (d) None of these 4. Digital devices are __________. (a) Digital clock (b) Automobile speed meter (d) Clock with a dial and two hands (d) All the above CU IDOL SELF LEARNING MATERIAL (SLM)

Classification of Computers 63 5. The computer that process both analog and digital is called __________. (a) Analog computer (b) Digital computer (c) Hybrid computer (d) Mainframe computer 6. Mnemonic a memory trick is used in which of the following language? (a) Machine language (b) Assembly language (c) High level language (d) None of these Answers: 1. (a), 2. (d), 3. (c), 4. (a), 5. (c), 6. (b) 3.10 References References of this unit have been given at the end of the book.  CU IDOL SELF LEARNING MATERIAL (SLM)

UNIT 4 STORAGE DEVICES Structure: 4.0 Learning Objectives 4.1 Introduction 4.2 Block Diagram of a Computer 4.3 Computer Memory 4.4 Main Memory 4.5 Secondary Memory 4.6 Summary 4.7 Key Words/Abbreviations 4.8 Learning Activity 4.9 Unit End Questions (MCQs and Descriptive) 4.10 References 4.0 Learning Objectives After studying this unit, you will be able to:  Understand the concepts of Hardware and Software  Understand the concepts of Computer Memory and Secondary Memory

Storage Devices 65 4.1 Introduction Hardware is a physical part of computer that causes processing of data. Software is a set of instruction that tells a computer exactly what to do. It is manufactured. It is developed and engineered. Hardware cannot perform any task without software. For example, the computer monitor you are using to read this text and the mouse you are using to navigate this web page are computer hardware. 4.2 Block Diagram of a Computer All computer systems, no matter how small or large, have the same fundamental capabilities: • Input Device: It includes devices like keyboard and mouse, which are used by the user to give some data to the computer. • Central Processing Unit: Processing unit is where these data are processed and turned into meaningful information. It also includes temporary storage (RAM) in which the data currently being processed are stored temporarily. • Output Device: To show the result of processes, to the user, output devices like monitors and printers are used. CU IDOL SELF LEARNING MATERIAL (SLM)

66 Computer Fundamentals Following are the figure of block diagram of a computer: Central Processing Unit* INPUT MEMORY UNIT OUTPUT Data & hold the data, instruction information Instruction and result of processing with result CONTROL UNIT Interpret stored instruction sequence issue command to all element ARITHMETIC LOGIC UNIT Perform arithmetic and Logic operation SECONDARY STORAGE Fig. 4.1: Block Diagram of a Computer Input Device Explanation for input device is given in unit 5. Central Processing Unit (CPU) The Central Processing Unit (CPU) is the component of a computer system with the circuitry to control the interpretation and execution of instructions. It performs the process part of INPUT- PROCESS-OUTPUT cycle. A CPU built on a single chip is called a ‘Microprocessor’. A microprocessor is an electronic device which is of little use unless interfaced with memories and several other Input/Output (I/O) device. CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 67 Fig. 4.2: Central Processing Unit (CPU) Nowadays, microprocessor is also called ‘Processor’. Aprocessor combined with main memory, auxiliary storage, input device and output device, which make a computer. A microprocessor incorporates most or all of the functions of a computer’s CPU on a single Integrated Circuit (IC). ICs are made up of different electronic components such as capacitors, resistors, transistors, etc. Fig. 4.3: Motherboard Fig. 4.4: Integrated Circuit (IC) These components are hooked together on fiberglass boards called circuit boards. You can see the small thin copper or metal lines (wires) on a circuit board that connect the different components together. These are called traces. Integrated Circuit is also called microchip. In a microcomputer, the printed circuit board that connects all of the parts of the computer together is called the CU IDOL SELF LEARNING MATERIAL (SLM)

68 Computer Fundamentals ‘motherboard’. The CPU could be considered the ‘brain’ of the computer. It sends electrical signals to the various parts of the computer, controlling what goes on. The motherboard contains the CPU, as well as a separate chip for the system clock. Everything connected to your computer system, plugs either directly or indirectly into the motherboard. The motherboard contains the CPU, the BIOS ROM chip (Basic Input/Output System), and the CMOS Setup information. It has expansion slots for installing different adapter cards like video card, sound card, Network Interface Card and modem. It is sometimes called the system board, the logic board, the baseboard, or less commonly, the planar board. A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are cached memory locations, the average latency of memory accesses will be closer to the cache latency than to the latency of main memory. When the processor needs to read from or write to a location in main memory, it first checks whether a copy of that data is in the cache. Then the processor immediately reads from or writes to the cache, which is much faster than reading from or writing to main memory. CPU Structure As there are a great many variations in architecture between the different kinds of CPU, a simplified model of the structure is looking here. The simplified model consists of five parts: • Control Unit • Arithmetic and Logic Unit (ALU) • Register Array • System Bus • Memory Unit CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 69 Fig. 4.5: CPU Structure (a) Control Unit The Control Unit interprets any instruction it receives from memory and directs the sequences of events necessary to execute the instruction. It is also responsible for performing the instruction execution cycle. It consists of a decoder, control logic circuits and a clock to ensure everything happens at the correct time. Control unit uses a system clock which synchronizes all tasks by sending out electrical pulses. The clock speed of a CPU is defined as the frequency that a processor executes instructions or that data is processed. This clock speed is measured in millions of cycles per second or megahertz (MHz) and is the main element in determining the speed of the processor. Computer speed is also measured by the ‘Number of Instructions Completed Per Second’ or ‘Millions Per Second (MPS)’ or ‘Instructions Per Second (MIPS)’. Hertz is the unit of frequency that measures the number of cycles per second in a periodic signal. CU IDOL SELF LEARNING MATERIAL (SLM)

70 Computer Fundamentals Fig. 4.6: Control Unit (b) Arithmetic and Logic Unit The Arithmetic and Logic Unit (ALU) is that part of CPU where actual data processing occurs. All calculations (mathematical) and all comparisons (logic function) take place in this unit. Basic arithmetic functions which an ALU can carry out are addition and subtraction. More powerful CPUs can support additional mathematical operations like multiplication and division. Fig. 4.7: Arithmetic and Logic Unit In addition to arithmetic functions, the ALU also performs logic functions. The logical operation which can it can carry out greater than, equal to, less than comparison between two numbers. Besides these operations, some processors also supports operations which check if particular bits are on or off. The ALU is made up of devices called gates that receive one or more inputs and based upon what function they are designed to perform, output a result. The ALU in example performs one of seven functions: NOT, Left Shift, Right Shift, Add, Subtract, AND, OR. Every arithmetic step requires at least two numbers and then it produces a result. Multiplication, for example, uses a multiplicand and a multiplier to get a product. Although every ALU must be able CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 71 to manage the two data words and the result, different processing and storage techniques are used in different models. (c) Register Array Registers are temporary memory units that store a computer instruction, a storage address or any kind of data (such as a bit sequence or individual characters). The registers are located in the processor, instead of in RAM, so data can be accessed and stored faster. When a program is debugged, register contents may be analyzed to determine the computer’s status at the time of failure. Each of the registers is 16 bits long, i.e., can contain a 16-bit binary number. Group of flip flops and gates form a register. Register is a special purpose memory. This memory is vital for moving data in and out of the main memory and to process the data. When CPU executes the instructions, there is a transfer of information between various units of the computer system. CPU uses these registers to handle the process of execution effectively and efficiently. They are a part of the central processing unit but cannot be considered as a part of main memory. They can hold only one piece of data at a time. Registers receive the information, hold it temporarily and pass it on as directed by the control unit. The number of registers varies from computer to computer, each one designed to perform a specific function. Types of Registers A processor often contains several kinds of registers, that can be classified according to their content or instructions that operate on them: (i) User-accessible registers are divided into data registers and address registers. (ii) Data registers are used to hold numeric values such as integer and floating-point values. (iii) Address registers hold addresses and are used by instructions that indirectly access memory. (iv) Index register are used to store the index of memory address. (v) Conditional registers hold truth values often used to determine whether some instruction should or should not be executed. CU IDOL SELF LEARNING MATERIAL (SLM)

72 Computer Fundamentals (vi) General purpose registers (GPRs) are combined with Data and Address registers. They can be used by the programmer for data manipulation. (vii) Floating point registers (FPRs) are the type of data registers that store floating point numbers in many architectures. (viii) Accumulator register is special data register which stores the result of the last processing step of the ALU. (ix) Constant registers are used to store read only values such as zero, one, or pi. (x) Vector registers hold data for vector processing done by SIMD instructions (Single Instruction, Multiple Data). (xi) Special purpose registers (SPRs) hold program state. This have two special registers – Status Registers and Control Registers. (xii) Status registers has two special registers – • Stack Pointer: Contains the last address of a stack of. • Status Register: Also flag register or condition code register (CCR)) is a collection of flag bits for a processor. (xiii) Control registers has two special registers – • Program Counter (PC): Contains the address (in binary) in main memory of the next instruction. • Instruction Register (IR): Contains the instruction (in binary) that is currently being executed. (xiv) Model-specific registers (also called machine-specific registers) store data and settings related to the processor itself. (d) System Bus The system bus is a cable which carries data communication between the major components of the computer, including the microprocessor. These wires carry information in terms of voltage. If CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 73 5V at a wire indicates Bit 1, 0V indicate Bit 0. The system bus consists of three different groups of wiring, called the data bus, control bus and address bus. These all have separate responsibilities and characteristics, which can be outlined as follows: (i) Address Bus An address bus carries the address of memory location or address of the peripheral. If the computer used 8 bits to represent the address of a location, then it can address upto 28 – 256 location. Sometimes, the address bus is combined with the data bus also. This is said to be address bus multiplexed with data bus. Bits flow from the microprocessor to peripheral is undirectional. (ii) Data Bus A Data Bus carries the data to the memory location or input/output units. In 8-bit computer, the width of the Bus is 8 lines. It can carry only 8-bits at a time. The control unit will distinguish whether the data is to be sent for input or output. Data flow between microprocessor and memory and peripheral is bidirectional. (iii) Control Bus This Bus carries control signals used to control overall operations of the computer. This Bus sends appropriate signals at the appropriate time to all the parts of the computer. These provide timing and control signals. (e) Memory Unit The memory is not an actual part of the CPU itself, and is instead housed elsewhere on the motherboard. However, it is here that the program being executed is stored, and as such is a crucial part of the overall structure involved in program execution. For more information about memory, please see next pages. Output Device Explanation for output device is given in unit 5. CU IDOL SELF LEARNING MATERIAL (SLM)

74 Computer Fundamentals 4.3 Computer Memory In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory (RAM), which is fast but temporary storage. Storage today more commonly refers to mass storage — optical discs, forms of magnetic storage like hard disk drives, , which is slower than RAM, but of a more permanent nature. Historically, memory and storage are respectively called ‘main memory’ or ‘primary storage’ or ‘internal memory’ and ‘secondary storage’ or ‘external memory’. 4.4 Main Memory Primary or Main Memory A storage location that holds memory for short periods of times. RAM and ROM are examples of a primary storage device. This storage unite is often called either ‘main memory’ or ‘primary memory’. The primary memory of CPU is the place where computer program and data is stored during processing. Fig. 4.8: Primary or Main Memory Random Access Memory (RAM) Pronounced ram, acronym of Random Access Memory, a type of computer-memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. This is the memory that the computer uses while it is executing programs. RAM is the most common type of memory found in computers and other devices, such as printers. CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 75 Fig. 4.9: Random Access Memory (RAM) Read-Only Memory (ROM) Pronounced ROM, acronym for Read-Only Memory, a computer memory on which has been prerecorded. The information stored on the ROM, chips is permanent and is stored when it is manufactured. Unlike the main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile whereas RAM is volatile. Fig. 4.10: Read-Only Memory (ROM) Most personal computers contain a small amount of ROM that stores critic programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs. A variation of a ROM is the PROM (programmable read-only memory). PROMs are manufactured as blank chips on which data can be written. CU IDOL SELF LEARNING MATERIAL (SLM)

76 Computer Fundamentals 4.5 Secondary Memory Secondary Storage Device A storage medium that holds information until it is deleted or overwritten. The memory capacity of the computer can be increased by using secondary or external or auxiliary memory units to the computer. This is the additional memory used to supplement the storage capability. It is less expensive and more flexible than main memory. These devices store information such as software and data permanently. For example, magnetic disk, magnetic tapes, etc. Magnetic Tape They are convenient, inexpensive devices which can be used to store large volumes of data. The magnetic tape is similar to the commonly used audio tape recorders. The tape is wound on a spool and threaded manually on the take-up spool. Data on tapes is stored as blocks, therefore recording and retrieving is sequential. The access time in the case of magnetic tapes is quite high. Fig. 4.11: Magnetic Tape Magnetic Disks A magnetic disk is a circular platter that is made of smooth metal or mylar plastic. It is coated with magnetic material. Data is stored or retrieved from the disk using a conducting coil called the head. During read/ write, the head is stationary while the platter rotates beneath it. With disks, it is possible to directly CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 77 access records by specifying the address or location. That is why disks are called direct access storage devices. Fig. 4.12: Magnetic Disk Hard Disk Hard disk is a magnetic disk on which one can store computer data. The hard disk is faster than floppy disks. For example, hard disk can store anywhere from one megabytes to several gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes. A single hard disk usually consists of several platters. Each platter requires two read/write heads, one of each side. All the read/write head are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders. In general, these are less portable than floppies, although it is possible to buy removable hard disks. There are two types of removable hard disks, disk packs and removable cartridges. Fig. 4.13: Hard Disk CU IDOL SELF LEARNING MATERIAL (SLM)

78 Computer Fundamentals Winchester Disk Another magnetic media suitable for large volumes of information is the hard disk popularly known as Winchester disk. A Winchester disk pack consists of two or more magnetic plates fixed to a spindle, one below the other with a set of read-write heads. The disk pack is permanently seated inside a casing to protect it from dust and other contamination, thus, increasing its reliability and data integrity. They can hold large volume of information than floppies. They are very fast in reading and writing. Winchester disks are available in different sizes and capacities. Standard sizes are 5.25 inches, 8 inches, 10.5 inches and 14 inches, storage capacities. These is a portable memory device that can be used to quickly transfer to audio, video and data files from the hard drive of one computer to another. Fig. 4.14: Winchester Disk Optical disk Optical disks differ from magnetic disks by the way data is stored and read. In optical disks, a laser beam is used to read and write data on these reflective disks. They support direct access to data and have more storage capacity than magnetic disks. They are popularly known as compact disks (CDs). CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 79 Optical disks can store much more data upto 6 gigabytes (6 billion bytes) than magnetic media, such as floppies and hard disks. It is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. The laser beam reads the pits and the data can be accessed. There are three basic types of optical disks Fig. 4.15: Optical Disk Optical Storage Devices Compact Disc Compact Disc (CD) is a Secondary Storage device. We can store the data, and information to the disc of size 700 MB and above. It is pronounced as “see-dee” ROM. There are various types – Read-Only Memory CD-ROM PROM, EPROM, CD-R Drive, CD-RW Drive, etc. CU IDOL SELF LEARNING MATERIAL (SLM)

80 Computer Fundamentals Fig. 4.16: Compact Disc CD-ROM A CD-ROM is a CD that contains computer data, which cannot be read or rewritten. In computers, CD-ROM is the most commonly used optical storage technology. CD-ROM is a compact disc that contains information, which is accessible by a computer. It is composed of polycarbonate plastic, thin reflective metal layers, made of aluminum and a lacquer coating. Data is stored on the disc as a series of light and dark pits; the light portion refers to the spaces between the pits. A laser beam reads the pits and the data can be accessed. CD-ROM is an adaptation/EXTENSION of the compact disc that is designed for music storage and playback. The format of CD-ROM is very similar to an audio CD; the only difference being the standards used to store data. A standard 120 mm CD-ROM holds up to 700 MB of data, or about 70 minutes of audio. This may mean that one CD can contain over one thousand novels; an average novel being composed of 60, 000 words. A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages. Once the data is written to a standard CD- ROM disc, it cannot be altered or rewritten. CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 81 Fig. 4.17: CD-ROM 4.6 Summary Hardware is a physical part of computer that causes processing of data. Software is a set of instruction that tells a computer exactly what to do. It is manufactured. It is developed and engineered. Hardware cannot perform any task without software. The central processing unit (CPU) is the component of a computer system with the circuitry to control the interpretation and execution of instructions. It performs the process part of input-process- output cycle. Control unit uses a system clock which synchronizes all tasks by sending out electrical pulses. The clock speed of a CPU is defined as the frequency that a processor executes instructions or that data is processed. The ALU is made up of devices called gates that receive one or more inputs and based upon what function they are designed to perform, output a result. The ALU in example performs one of seven functions: NOT, Left Shift, Right Shift, Add, Subtract, AND, OR. Registers are temporary memory units that store a computer instruction, a storage address or any kind of data (such as a bit sequence or individual characters). In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory (RAM), which is fast but temporary storage. CU IDOL SELF LEARNING MATERIAL (SLM)

82 Computer Fundamentals A storage location that holds memory for short periods of times. RAM and ROM are examples of a primary storage device. This storage unite is often called either ‘main memory’ or ‘primary memory’. A storage medium that holds information until it is deleted or overwritten. The memory capacity of the computer can be increased by using secondary or external or auxiliary memory units to the computer. 4.7 Key Words/Abbreviations  Central Processing Unit (CPU): The Central Processing Unit (CPU) is the component of a computer system  Control Unit: The Control Unit interprets any instruction it receives from memory.  Arithmetic and Logic Unit: The ALU is made up of devices called gates that receive one or more inputs  Register Array: The registers are located in the processor, instead of in RAM, so data can be accessed and stored faster.  Memory Unit: The memory is not an actual part of the CPU itself, and is instead housed elsewhere on the motherboard. 4.8 Learning Activity 1. What is CPU? Explain the CPU structure. —————————————————————————————————— —————————————————————————————————— 2. Explain different types of secondary devices with example. —————————————————————————————————— —————————————————————————————————— CU IDOL SELF LEARNING MATERIAL (SLM)

Storage Devices 83 4.9 Unit End Questions (MCQs and Descriptive) A. Descriptive Type Questions 1. What is Control Unit? 2. Discuss about Arithmetic and Logic Unit. 3. Explain the types of Registers. B. Multiple Choice/Objective Type Questions 1. The brain of any computer system is __________. (a) Control Unit (b) Arithmetic Logic Unit (c) Central Processing Unit (d) Storage Unit 2. ALU is __________. (a) Arithmetic Logic Unit (b) Array Logic Unit (c) Application Logic Unit (d) None of these 3. Which of the following is a secondary memory device? (a) Keyboard (b) Disk (c) ALU (d) All the above 4. Pick the one that is used for logical operations or comparisons such as less than equal to or greater than. (a) Arithmetic and Logic Unit (b) Control Unit (c) Both [a] and [b] (d) None of these CU IDOL SELF LEARNING MATERIAL (SLM)

84 Computer Fundamentals 5. __________ are used to hold numeric values such as integer and floating-point values. (a) Data registers (b) Index registers (c) Conditional registers (d) Accumulator registers 6. __________ are used to store read only values such as zero, one, or pi. (a) Index registers (b) Constant registers (c) Accumulator registers (d) Conditional registers Answers: 1. (c), 2. (a), 3. (b), 4. (a), 5. (a), 6. (b) 4.10 References References of this unit have been given at the end of the book.  CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 85 UNIT 5 HARDWARE AND SOFTWARE Structure: 5.0 Learning Objectives 5.2 Elements of Computer – Hardware and Software 5.3 Relationship between Hardware and Software 5.4 Computer Peripherals 5.5 Input Devices 5.6 Output Devices 5.7 Software Requirements 5.8 Summary 5.9 Key Words/Abbreviations 5.10 LearningActivity 5.11 Unit End Questions (MCQs and Descriptive) 5.12 References CU IDOL SELF LEARNING MATERIAL (SLM)

86 Computer Fundamentals 5.0 Learning Objectives After studying this unit, you will be able to:  Understand the concept of Computer Peripherals  Explain the Output Devices of computer  Discuss Software requirements for computer 5.1 Introduction A computer peripheral is any external device that provides input and output for the computer. For example, a keyboard and mouse are input peripherals, while a monitor and printer are output peripherals. A computer peripheral is a device that is connected to a computer but is not part of the core computer architecture. The core elements of a computer are the central processing unit, power supply, motherboard and the computer case that contains those three components. Technically speaking, everything else is considered a peripheral device. However, this is a somewhat narrow view, since various other elements are required for a computer to actually function, such as a hard drive and random access memory (or RAM). Most people use the term peripheral more loosely to refer to a device external to the computer case. You connect the device to the computer to expand the functionality of the system. For example, consider a printer. Once the printer is connected to a computer, you can print out documents. Another way to look at peripheral devices is that they are dependent on the computer system 5.2 Elements of Computer – Hardware and Software Generally, the basic elements of computer are ‘hardware’ and ‘software’, which are frequently used in computer system. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 87 Computer Hardware Software Input CPU Output System Application device device Software Packages * MS Word Processor Memory Supporting Operating Programming * MS Excel Electronic System Language * MS Access * Multimedia * Windows * C * Potoshop * Tally Primary Secondary * Windows NT * C++ * Pagemaker * DOS * Java * Unix * Visual Basic Temporary Permanent * Pascal * Basic Low capacity High capacity Very fast Slow scan speed Scan speed Voltile Non Voltile RAM Harddisk Floppy Disk CD Rom Fig. 5.1: Hardware and Software The hardware consists of the physical equipments which makes up the computer system like Monitor, Keyboard, CPU, Hard Disk, Floppy drive, Printer etc. Normally all the items which can seen and touched are hardware items. Thus, storage, processing and control unit, I/O device (input/ output device) and peripherals devices – all are hardware. It is the physical part of the computer including the digital circuits inside the computer. Hardware includes not only the computer parts but CU IDOL SELF LEARNING MATERIAL (SLM)

88 Computer Fundamentals also the cables, connectors, power supply units and peripheral devices such as the keyboard, mouse, audio speakers and printers. Entering and displaying information is carried out on a wide variety of accessory devices called peripherals, also known as input/output (I/O) devices. Some peripherals, such as keyboard is only input devices, other peripherals, such as printer is only output devices and some are both. The term ‘software’ was first used by John W. Tukey in 1958 as the following sense – “In computer science and software engineering, computer software is all computer programs”. The most modern software theory was first proposed by Alan Turing in 1935 is – “Computer software, consisting of programs, codes or instructions that enables a computer to perform specific tasks”. Software is an ordered sequence of instructions for changing the state of the computer hardware in a particular sequence. In computers, software is loaded into RAM and executed in the central processing unit. 5.3 Relationship between Hardware and Software Computer software and computer hardware can exist independently of each other, just as a human soul and a human body. The human body does nothing when not indwelt by a soul and the human soul is inaccessible to us on earth after it has separated from its body in death. Fig. 5.2: Relationship between Hardware and Software Likewise, a  computer  program  (software)  cannot  operate  without  the  computer  hardware. The hardware also cannot perform the processes that the software is programmed to perform, CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 89 unless it has had access to the software to gain the needed instructions. ”A computer requires programs to function and a computer program does nothing unless its instructions are executed by a central processor” (“Computer Program”). 5.4 Computer Peripherals When you look at a computer closely, the following main parts are: Mouse A mouse is used to replace the key combinations with easier point and click actions. The mouse is connected to the main board of the computer by a cable. It is input device. Keyboard A computer keyboard is a typewriter-style device which uses an arrangement of buttons or keys to act as a mechanical lever or electronic switch. It enables to enter data into a computer and other devices. Monitor Monitor is a display screen used to provide visual output from a computer. It uses CRT and LCD technologies. Hard Disk Drive (HDD) A hard disk drive (HDD, hard disk, hard drive or fixed disk) is a data storage device that is used to store files for the operating system and software that run on the computer, as well as files created or downloaded to the computer by a user. CPU (Central Processing Unit) A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and input/ output (I/O) operations specified by the instructions. CPU is the brains of the computer. Printer In computers, a printer is a device that accepts text and graphic output from a computer and transfers the information to paper, usually to standard size sheets of paper. CU IDOL SELF LEARNING MATERIAL (SLM)

90 Computer Fundamentals 5.5 Basic Input System An input device is a peripheral used to provide data and control signals to an information processing system such as a computer or information appliance. Examples of input devices include keyboards, mouse, scanners, digital cameras and joysticks etc. Each of the device is explained below. Keyboard Keyboard was the first input device to be used with computers and it is still the major and most widely used among all the input devices. It is the primary input device for entering text and numbers. It is an arrangement of keys on a board in an organized way – this is why it is called keyboard. A keyboard is connected to a computer system using a cable or a wireless connection. A standard keyboard has 102 to 110 keys and with 256 to 260 characters and each key sends a different signal to the CPU. When a key is pressed, a tiny chip called the keyboard controller notes that a key has been pressed. Then the keyboard controller places a code into the keyboard buffer to indicate which key is pressed and sends a signal to the computer’s system software to tell that something has happened at the keyboard. When the system software receives the signal, then it reads the memory location in the keyboard buffer that contains the code of the pressed key. Then the system software passes the code to the CPU. The keyboard buffer can store many keystrokes at one time. Fig. 5.3: Keyboard The Basic PC Keyboard Layout A keyboard typically contains keys for individual letters, numbers and special characters, as well as keys for specific functions. There are four main keys on PC’s keyboard. CU IDOL SELF LEARNING MATERIAL (SLM)

Hardware and Software 91 Function keys: These keys are positioned on the top row of the keyboard which are labeled as F1, F2, F3, and on up to F11 and F12. Though F1 through F12 have some default primary and secondary features, they can be used well in combination with keys like Ctrl and Alt. F1: To open help window. F2: To used to rename a file or folder. Alt + Ctrl + F2 opens the Documents Library while on MS Office suite. F3: To used to find something. Shift + F3 toggles between capitalizing each word, lower case and upper case for selected text on MS Word. F4: Alt + F4 closes the current program. If no program is running then it launches the Shutdown dialog box. F5: To used to refresh action. While using PowerPoint it is used to start a slide show. Opens Find, Replace, Go to dialog on MS Office programs. F6: To focuses on the address bar. F7: To turns on browsing on Mozilla Firefox. F8: To enters the Windows Start Menu. F9: To compiles and runs the code in combination with Ctrl key. F10: To shows the Menu bar in Firefox and IE. F11: To opens full screen mode in Windows Explorer and all browsers. F12: To opens Save As window on MS Office. Typewriter keys: These keys are the same types of keys that find on an old typewriter. All letters, numbers, and punctuation symbols include: Cursor-control keys: These four arrow keys move the text cursor in the direction of their arrows. There are more six-pack cursor-control keys such as Insert, Delete, Home, End, Page Up and Page Down. CU IDOL SELF LEARNING MATERIAL (SLM)

92 Computer Fundamentals Numeric keypad: The numeric keypad contains calculator-like keys which are popular with accountants, bank tellers and airline ticket agents. Fig. 5.4: Typical Windows QWERTY keyboard Types of Computer Keyboard There are two major keyboard layouts being used worldwide: (i) Standard keyboard (qwerty): It is named after the first six leftmost letters on the top alphabetical line of the keyboard. Also called a QWERTY keyboard because of the layout on its typing area. It has about 103 keys and about 257 characters. (ii) Multimedia keyboard: It is designed for the user to access often-used programs such as Internet, music and email. It contains buttons that control various computer processes, such as turning on the computer's power, putting the CPU to sleep and waking it up again. It comes in various connection formats, including PS/2, USB and wireless. Types of Keys on a Computer Keyboard (i) Alphanumeric keys: All of the letters and numbers on the keyboard A-Z and 0-9. This arrangement is called the QWERTY because the first SIX keys on top of the row of letters CU IDOL SELF LEARNING MATERIAL (SLM)