Computer Hardware Systems Study 1 COSC 319 PDF

COMPUTER HARDWARE SYSTEMS STUDY 1  A COSC GENERAL 319 INTRODUCTION TO SYSTEMS; THE COMPUTER HARDWARE SYSTEM  COMPUTER PROCESSING METHODS  MULTIPLEXING/DEMULTIPLEXING  APPLICATION OF MUX/DEMUX: MODEMS, ADC, DAC  SYSTEM VIABILITY  GRACEFUL DEGRADATION  MTTR (MID-TIME TO REPAIR)  MTBF (MID-TIME BETWEEN FAILURE) DIGITAL LOGIC AND DESIGN BY ENGR. SAM O. OGUNLERE General Introduction to systems One can think of the systems approach as an organized way of dealing with a problem. Defining A System: A collection of components that work together to realize some objective forms a system. Fig. 1: Traditional Components of a System In a system, the different components are connected with each other and they are interdependent. The objective of the system demand that some output is produced as a result of processing the Definition of a System; characteristics An interrelated set of business procedures (or components) used within one business unit, working together for some purpose; Also a group of interrelated procedures used for a business function, with an identifiable boundary, working together for some purpose. E.g., a system in the payroll department keeps track of cheques, whereas an inventory system keeps track of supplies. The two systems are separate. Nine characteristics of a system, seven of which are shown in Figure 2, with a detailed explanation of each characteristic, shows that 1. Components 2. Interrelated components 3. Boundary 4. Purpose 5. Environment 6. Input 7. boundary A Constraintsseparates 8. Interfaces 9. Output the system from its environment. The system takes input from outside, processes it, and sends the resulting output back to its environment. The arrows in the figure show this interaction between the system and the world outside Fig. 2: Seven Characteristics of it. of a system A system is made up of components. A component is either an irreducible part or an aggregate of parts, also called a subsystem. The simple concept of a component is very powerful. For example, just as with an automobile or a stereo system, with proper design, we can repair or upgrade the system by changing individual components without having to make changes throughout the entire system. The components are interrelated; that is, the function of one is somehow tied to the functions of the others. For example, the work of one component, such as producing a daily report of customer orders received, may not progress successfully until the work of another component is finished, such as sorting customer orders by date of receipt. A system has a boundary, within which all of its components are contained and which establishes the limits of a system, separating it from other systems. Components within the boundary can be changed, whereas systems outside the boundary cannot be changed. All of the components work together to achieve some overall purpose for the larger system: the system’s reason for existing. A system exists within an environment—everything outside the system’s boundary that influences the system. For example, the environment of a state university includes prospective students, foundations and funding agencies, and the news media. Usually the system interacts with its environment. Just as a system interacts with its environment by receiving data (raw facts) and information (data processed in a useful format), a university also interacts with prospective students by having open houses and recruiting from local high schools. Figure 3 shows how a university can be seen as a system. The points at which the system meets its environment are called interfaces; an interface also occurs between subsystems. In its functioning, a system must face constraints—the limits (in terms of capacity, speed, or capabilities) to what it can do and how it can achieve its purpose within its environment. Some of these constraints are imposed inside the system (e.g., a limited number of staff available), and others are imposed by the environment (e.g., due dates or regulations). A system takes input from its environment in order to function. People, for example, take in food, oxygen, and water from the environment as input. You are constrained from breathing fresh air if you’re in an elevator with someone who is polluting the air. Finally, a system returns output to its environment as a result of its functioning and thus achieves its purpose. The system is constrained if electrical power is cut. It is therefore important to be familiar with different kinds of systems for at least two reasons: First of all, your work will probably focus on one kind of system, which will generally be a part of a larger system. For example, a payroll system, which is part of a larger “human resources” system, which is, in turn, part of an overall business organization (which is itself, a system), which is, in turn, part of a larger economic system, and so on. Fig. 3: A University as a system Thus, you must understand the other systems with which it will interact because many of the computer systems that we build are replacements, or new implementations of, non-computerized systems that are already in existence. Secondly, even though many types of systems appear to be quite different, they turn out to have many similarities. There are common principles and philosophies and theories that apply remarkably well to virtually all kinds of systems Thus, we can often apply to systems that we build in the computer field, what we have learned about other systems, based on our own day-to-day experience, as well as the experience of scientists and engineers in a variety of fields And now, we can consider a definition of the basic term "system". It provides several definitions: 2. An organized set of doctrines, ideas, or principles, usually intended to explain the arrangements or working of a systematic whole. 3. An organized or established procedure. 4. Harmonious arrangement or pattern: order. 5. An organized society or social situation regarded as stultifying establishment. COMMON TYPES OF SYSTEMS There are many different types of systems, but indeed, virtually everything that we come into contact with during our day-to-day life is either a system or a component of a system (both). Because our ultimate focus is on computer systems, we will divide all systems into two NATURAL SYSTEMS There are a lot of systems that are not made by people: they exist in nature and, by and large, serve their own purpose. It is convenient to divide natural systems into two basic subcategories: physical systems and living systems. Physical systems include such diverse example as: Stellar systems: galaxies, solar systems, and so on. Geological systems: rivers, mountain ranges, and so on. Molecular systems: complex organizations of atoms. Physical systems are interesting to study because Living systems encompass all of the myriad animals and plants around us, as well as our own human race. The properties and characteristics of familiar living systems can be used to help illustrate and better understand man-made systems. 1. The reproducer, which is capable of giving rise to other systems similar to the one it is in. 2. The boundary, which holds together the components that make up the system, protects them from environmental stresses, and excludes or permits entry to various sorts of matter-energy and information. 3. The Ingestor, which brings matter-energy across the system boundary from its environment. 4. The distributor, which carries inputs from outside the system or outputs from its subsystems around the system to each component. 5. The converter, which changes certain inputs to the 6. The producer, which forms stable associations that endure for significant periods among matter-energy inputs to the system or outputs from its converter, the materials synthesized being or growth, damage repair, or replacement of components of the system, or for providing energy for moving or constituting the system’s outputs of products or information markets to its suprasystem. 7. The matter-energy storage subsystem, which retains in the system, for different periods of time, deposits of various sorts of matter-energy. 8. The extruder, which transmits matter-energy out of the system in the form of products or wastes. 9. The motor, which moves the system or parts of it in relation to part or all of its environment or moves components of its environment in relation to each other. 10. The supporter, which maintains the proper spatial 11. The input transducer, which brings markers bearing information into system, changing them to other matter-energy forms suitable for transmission within it. 12. The internal transducer, which receives, from other subsystems or components within the system, markers bearing information about significant alterations in those subsystems or components, changing them to other matter- energy form of a sort that can be transmitted within it. 13. The channel and net, which are composed of a single route in physical space, or multiple interconnected routes, by which markers bearing information are transmitted to all parts of the system 14. The decoder, who alters the code of information input to it through the input transducer or internal 16. The memory, which carries out the second stage of the learning process, storing various sorts of information in the system for different periods of time. 17. The decider, which receives information inputs from all other subsystems and transmits to them information outputs that control the entire system. 18. The encoder, who alters the code of information input to it from other information processing subsystems, from a private code used internally by the system into a public code that can be interpreted by other systems in its environment. 19. The output transducer, which puts out markers bearing information from the system, changing markers within the system into other matter-energy forms that can be transmitted over channels in the system’s environment. Keep in mind that many man-made systems (and automated systems) interact with living systems. In some cases, automated systems are being designed to replace MAN-MADE SYSTEMS Man-made systems include such things as: 1. Social systems: organizations of laws, doctrines, customs, etc. 2. An organized, disciplined collection of ideas. 3. Transportation systems: networks of highways, canals, airlines, etc. 4. Communication systems: telephone, telex, and so on. 5. Manufacturing systems: factories, assembly lines, and so on. 6. Financial systems: accounting, inventory, general ledger and so on. Most of these systems include computers today. In most case, we will be in a position to determine whether it makes sense to use a computer to carry out the Automated systems Automated systems are the man-made systems that interact with or are controlled by one or more computers. There are many different kinds of automated systems, but they all tend to have common components: 1. Computer hardware (CPUs, disks, terminals, and so on). 2. Computer software: system programs such as operating systems, database systems, and so on. 3. Peopleware/Warmware: those who operate the system, those who provide its inputs and consume its outputs, and those who provide manual processing activities in a system. 4. Data: the information that the system remembers over a period of time. 5. Procedures: formal policies and instructions for operating the system. A more useful categorization of automated systems is as follows: 1. Batch system: A batch system is one which in it, the information is usually retrieved on a sequential basis, which means that the computer system read through all the records in its database, processing and updating those records for which there is some activity. 2. On-line systems: accepts input directly from the area where it is created. It is also a system in which the outputs, or results of computation, are returned directly to where they are required. E.g. When a user makes a change to the data stored in the computer, the system will automatically update and re-process: UMIS, Booking/Ticket reservation systems etc. 3. Real-time systems: A real-time system may be defined as one which controls an environment (control systems) by receiving data, processing them, and returning the results sufficiently quickly to affect the 4. Decision-support systems: These computer systems do not make decisions on their own, but instead help managers and other professional “knowledge workers” in an organization make intelligent, informed decisions about various aspects of the operation. Typically, the decision-support systems are passive in the sense that they do not operate on a regular basis: instead, they are used on an ad hoc basis, whenever needed. 5. Knowledge-based systems: The goal of computer scientists working in the field of artificial intelligence is to produce programs that imitate human performance in a wide variety of “intelligent” tasks. GENERAL SYSTEMS PRINCIPLES There are a few general principles that are of particular interest to people building automated information systems. They include the following: 1. The more specialized a system is, the less able it is to adapt to different circumstances. 2. The more general-purpose a system is, the less 3. The larger a system is, the more of its resources that must be devoted to its everyday maintenance. 4. Systems are always part of larger systems, and they can always be partitioned into smaller systems. 5. Systems grow. This principle could not be true for all systems, but many of the systems with which we are familiar do grow, because we often fail to take it into account when we begin developing the system. What is a Computer System? A machine that can be programmed to accept data (input), process it into useful information (output), and store it away (in secondary Generations of Computers The technological advancements in the development of computers are classified into distinct groups often referred to as the Computer Generations 1. The first generation is characterized by vacuum tubes or thermionic valves. These tubes made the computer to be unnecessarily big, dissipates a lot of energy and very slow. Examples are ENIAC (which used 18,000 vacuum tubes), EDVAC and UNIVAC. 2. The development of electronic transistors gave birth to the second generation of computers, as tubes were replaced by transistors in the construction of the computer. Hence, these computers were smaller in size, generated.... 3. The introduction of integrated circuits (IC) into the manufacturing of computers led to the third generation of computers, also known as Chips. Hence with this advance in technology, computers of this generation are lighter in weight, faster, more reliable and of course cost less, e.g. IBM System/360; which was introduced in 1964. Fig. 4: Integrated Circuit of a computer The tiny microprocessor shown here is the heart of the personal computer (PC). The rows of leg-like metal pins are used to connect the microprocessor.... 4.Further improvement on the degree of integration led to the fourth generation. This generation is characterized by the use of Large Scale Integration (LSI), meaning many components in a very small space. This further led to the reduction of physical size/components of the computer e.g. pocket calculators, digital watches, and some personal computers. 5.The advanced industrial robots are classified in the fifth generation. This generation is concentrating on the way computers are used, not on the electronic refinement that characterized the previous four. Rather than processors of data, computer programs called Expert Systems are widely used. A.I., Neural Networks, Bio-informatics, robots, etc., are examples of fifth generation of computers. COMPUTER STRUCTURE...?? A computer follows input-process- output cycle, first the stage is performed in computer by input unit, second stage is performed by its central processing unit and the third stage is performed by output unit. Thus this is the basic structure of a computer. Components of a Computer 3. The program currently being executed is stored here. (it is divided into storage units called BYTES) 2. For reading data into Main Memory MAIN MEMORY 4. For permanent storage of programs and data INPUT DEVICES PROCESSOR OUTPUT DEVICES 1. For processing the data AUXILIARY STORAGE 5. For printing, displaying Fix Or out-put of info The Mistakes Components of a Computer The program currently being executed is stored here. (it is divided into storage units called BYTES) For processing the data MAIN MEMORY For printing, displaying Or out-put of info INPUT DEVICES PROCESSOR OUTPUT DEVICES For reading data into AUXILIARY Main Memory STORAGE For permanent storage of programs and data QUIZ 1 What do you think will be the focus point of a system? List 9 characteristics of systems Give a breakdown analysis of natural systems Differentiate between an online system and a real time system with an example each. List the major advancement in technology for each generation of computers. 1. What do you think will be the focus point of a system? To produced some output as a result of processing the suitable inputs 2. List 9 characteristics of systems 1. Components 2. Interrelated components 3. Boundary 4. Purpose 5. Environment 6. Interfaces 7. Constraints 8. Input 9. Output 3. Give a breakdown analysis of natural systems – physical systems (Stellar, Geological, and Molecular systems) and living systems (plants, animals and the human race). 4. Differentiate between an online system and a real time system On-line systems: An on-line systems is one which accepts input directly from the area where it is created. It is also a system in which the outputs, or results of computation, are returned directly to where they are required. E.g. When a user makes a change to the data stored in the computer, the system will automatically update and re-process: UMIS, Booking/Ticket reservation systems etc. Real-time systems: A real-time system may be defined as one which controls an environment (control systems) by receiving data, processing them, and returning the results sufficiently quickly to affect the environment at that time. E.g. ABS, TCS, Burglar alarms etc. 5. List the major advancement in technology for each generation of computers – 1st Gen: Thermionic valves or vacuum tubes; 2nd Gen: Electronic Transistors or switches; 3rd Gen: Integrated Circuits or Chips; 4th Gen: LSI; 5th Gen: How we use our computers rather than on their electronic refinements The Computer Hardware System The Computer H/W System INPUT PROCESSING OUTPUT AUXILIARY OR SECONDARY STORAGE UNIT UNIT UNIT UNIT CATEGORIES: CATEGORIES: CATEGORIES: CATEGORIES: KEYBOARDS – Control PRINTERS – STORAGE – Standard and Unit Impact and Non – Magnetic Tapes, Enhanced Impact Printers Disk, and Drums, ALU Keyboards Punch Cards, Zip MONITORS – and Diskette Memory POINTING – CRT, LCD, Gas Unit – RAM Drives, Flash Light pen, Mouse, Plasma & ROM Drives and T- Touch screens OPTICAL – Cards, OPTICAL – Projectors, CD-ROM/RW, Scanner, DigiCam Holograms DVD-ROM/RW, Internal & Ext. SOUND – Mic, SOUND – HDD, etc Microphones, Earphones, Fig. 5: The Computer Hardware System MIDI Loudspeakers MICR, OCR, etc COMPUTER HARDWARE DEVICES They are: 1. Peripheral devices (Input, Output, and Auxiliary or Secondary Storage Devices) and 2. Processing Devices 1. Peripheral Devices: A peripheral device is an ancillary device used to put information into and get information out of the computer. It is also any device that can be shortchanged or replaced on a computer system. It is also refers to all input, output and auxiliary or secondary storage devices or it refers to all devices except for the CPU. A. INPUT DEVICES Input devices are the components of computer which are used to input or give data and instruction to the computer by the user. The input unit is responsible for taking input and converting it into computer 1. Peripheral Devices (A. Input Devices) Data Vs. Instruction 2+2=4 Types of Input Devices DATA Instruction Information I. The Key Board Keyboard is the type of input device which is used to give data and instruction with the help of some sort of keys (AlphaNumeric, Numeric keypad, Special, and Function keys.) to the computer by the user. Keyboards are of two types vis-à-vis Devoke and QWERTY 33 Fig. 6: Types of Keyboard 1. Peripheral Devices (A. Input Devices) II. Pointing Devices Pointing Devices are those device which are used to give data, instruction and to specify a position in a space. Types of Pointing Devices Mouse (Mechanical, Optical) Light Pen (Direct Input) Touch Pad / Track ball (Indirect) Joy Stick (Indirect Input) Touch screen (Direct Input), etc. Fig. 7: A mouse 34 1. Peripheral Devices (A. Input Devices) III. Optical Devices Optical devices are used to give data in the shape of image. Types of Optical Devices Digital Camera Scanner Fig. 8: A Scanner IV. Audio Input Devices They are used to give data to the computer in the form of sound wave input. Microphones allow users to speak to the computer in order to record a voice message or navigate software Types of Audio Input Devices Microphone Mic MIDI (Musical Instrument Digital Interface) 35 All Examples of? INPUT DEVICES 1. Peripheral Devices (B. Output Devices) Output units gives out or display information for us to see and use. Types of Output Devices I. Display Devices Display devices are used to get result/information from the computer in Soft Copy. Monitor: A Monitor is a display output device which gives the result/information in text, images, video, or any other format. 37 1. Peripheral Devices (B. Output Devices) I. Display Devices Display devices are used to get result/information from the computer in Soft Copy. Monitor Monitor is an output device which gives the result/information in text, images, video, or any other format. Types of Monitor According to Size 14” 15” 17” 19” 21” diagonal shape measurement Types of Monitor According to Technology CRT (Cathode Ray Tube): Streams of electrons make phosphors glow on a large vacuum tube. LCD (Liquid Crystal Display): A flat panel display that uses crystals to let varying amounts of different colored light to pass through it. Developed primarily for portable computers. (Liquid Material between two layers of Glass) Gas Plasma Neon Oxen 39 Fig.9a&9b: Types of monitor according to technology Types of Monitor According to Colors Monochromes which contains only one color on its background Gray Scale Monitor it contains only two colors one is black and the other is White Color Monitor it contains 16~16 million colors (2^24 = 16,777,216 possible colors) High Resolution Costly 40 1. Peripheral Devices (B. Output Devices) II. Audio Output Devices – Windows machines need special audio card for audio output. – Audio output is useful for: Music – CD player in a computer. – Most personal computers have CD players that can access both music CDs and DVD-ROMs/RWs. Voice synthesis (sounding more human-like.) Multimedia 1. Peripheral Devices (B. Output Devices) III. Printers: Printer is the type of output device which is used to get the result/information in the shape of hardcopy from the computer. Types of Printer a) Impact Printer It prints characters or images by striking e.g. Dot Matrix Printer, Line Printer, Daisy Wheel Printer b) Non-Impact Printer A non-impact printer print characters and graphs on a piece of paper without striking. 42 1. Peripheral Devices (B. Output Devices) Types of Non-Impact Printer includes Inkjet Printer, LASER (Light Amplification by Stimulated Emission of Radiation), Thermal Printer, Photo Printer, etc. IV. Optical Devices Fig. 10: Non-impact Printers Examples include: 1. Projectors (An optical device that projects or casts a beam of light of images unto a screen), 2. Holograms (Holography:- A technique in physics for recording and then reconstructing the amplitude and phase distributions of a coherent wave disturbance; used to produce three-dimensional images), etc. 43 1. Peripheral Devices (C. Storage Devices) Storage Devices are used to store data on permanent or temporary basis. An Auxiliary storage is also called SECONDARY MEMORY, BACKING STORE, EXTERNAL MEMORY Types of Storage Devices Magnetic Devices Magnetic Tapes, Hard Disk (Winchester drive), Floppy Disk, etc. Optical Devices CD-ROM, CD-RW; DVD-ROM, DVD-RW 44 Other types of storage include Flash Memory Cards, 1. Peripheral Devices (C. Storage Devices)  Secondary storage is needed because  Main memory stores data temporarily  Main memory space is limited Benefits of secondary storage Space Storage Memory Reliability Type Floppy Disc 1.44 MB Convenience CD-Rom ~650MB Economic Memory Stick 256 MB ~ 32 GB (standard) DVD ~ 4 GB Hard Disc 40 Gig ~ 8TB 1. Peripheral Devices (C. Storage Devices) Many different consumer electronic devices can store data. A reel-to-reel tape recorder (Sony TC- 630). The magnetic tape is a data storage medium, while the recorder is a data Edison cylinder phonograph ca. storage equipment using 1899. The Phonograph cylinder is a portable medium (tape a storage medium. The reel to store the data. phonograph may or may not be considered a storage device. Internal Hard Drive pin Molex 4 connector Jumper pin Data 40 Setting Cable connector 48 The Future of Storage? 2. PROCESSING DEVICE: The Central Processing Unit (CPU) Processing devices are also the components of computer which are used to process the data and convert into information. The CPU is the control centre of the computer, as it guides, directs and governs its performance. It is the brain of the computer. The processor processes instructions in three steps: 1. Fetches Instructions 2. Decodes Instruction 3. Executes Instruction Either chips or integrated circuits, they are also found in almost every modern electrical device such as cars, television sets, CD players, cellular phones, etc. What is a Processor? Most computers use integrated chips….or integrated circuits for their processors or main memory A chip is about 1cm square…and can hold MILLIONS of electronic components such as transistors and resistors The CPU of a microcomputer is a microprocessor Processor and MAIN MEMORY of a PC are held on a single board called a motherboard. Types of Processors INTEL CHIP A computer chip is an electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material; hence the name Integrated Circuits or IC”s or simply Chips. An electric circuit is made from different electrical components such as transistors, resistors, capacitors and diodes, that are connected to each other in different ways. These components havelike a different The transistor acts switch behaviours. Resistor –resists electricity –so you can control current Capacitor –controls electricity Diode –also allows control of current and flow The Central Processing Unit (CPU) The CPU has three components which are responsible for different functions. They are: 1. Control unit (CU, Bus, Registers) 2. Arithmetic Logical Unit (ALU) 3. Memory Unit 1. CONTROL UNIT (CU) It is responsible for directing and coordinating most of the computer system activities. It does not execute instructions by itself It tells other parts of the computer system what to do CPU:1. CONTROL UNIT (CU) It determines the movement of electronic signals between the main memory and arithmetic logic unit as well as the control signals between the CPU and input/output devices. The term Bus refers to an electrical pathway through which bits are transmitted between the various computer components, and depending on the design of the system, several types of buses may be present. Types of Computer BUS 1. Data Bus The electrical path through which data is transferred between/among components of the computer Types of Computer BUS 2. Address Bus Each component is assigned a unique ID, this ID is called the address of that component. Components communicate and locate other components with this bus. 3. Control Bus Control bus is used to transmit different commands from one component to another component, i.e. CPU wants to read data from main memory, it use control bus for giving commands. 4. Expansion Bus The expansion bus allows the processor to communicate with the peripheral devices attached to the card. Types of Expansion Bus ISA (Industry Standard Architecture) Bus Local/PCI (Peripheral Component Interface) Bus AGP (Accelerated Graphics Port) Bus 59 CPU:1. CONTROL UNIT (REGISTERS) Register is a small, high-speed memory that resides inside a CPU. The CPU contains a number of Register, and Big size of register increases the performance of computer. Registers quickly, accept, store and transfer data and instructions that are being used immediately (main memory hold data that will be used shortly, cache memory stores frequently or recently used instructions, secondary storage holds data that will be used later) To execute an instruction, the control unit of the CPU retrieves it from main memory and places it onto a register. The instruction or execution cycle refers to the retrieval of the instruction from main memory and Memory Hierarchy CPU:2. Arithmetic and Logic Unit (ALU) ALU performs all the arithmetic and logical functions i.e. addition, subtraction, multiplication, division and certain comparisons These comparisons include greater than, less than, equals to etc. The ALU controls the speed of calculations. Digital logic is a rational process for making simple “true” or “false” decisions based on the rules of Boolean algebra. “True” can be represented by a 1 and “false” by a 0, and in logic circuits the numerals appear as signals of two different voltages.... Boolean algebra is used to solve problems and process information in digital systems; it deals with logic, rather than calculating actual numeric values. Boolean algebra is based on the idea that logical propositions are either true or false, depending on the type of operation they describe and whether the variables are true or false. “True” corresponds to the digital value of 1, while “false” corresponds to 0. Logic circuits are used to make specific true-false decisions based on the presence of multiple true- false signals at the inputs. The signals may be generated by mechanical switches or by solid-state transducers. CPU:2. Arithmetic and Logic Unit (ALU) The various families of digital logic devices, usually integrated circuits, perform a variety of logic functions through logic gates, including “OR”, ”AND”, and “NOT”, and combinations of these (such as “NOR”, which includes both OR and NOT). One widely used logic family is the transistor-transistor logic (TTL). A method of constructing electronic logic circuits. Another family is the complementary metal oxide semiconductor logic (CMOS), which performs similar functions at very low power levels but at slightly lower operating speeds. Several other, less popular families of logic circuits exist, including the currently obsolete resistor-transistor logic (RTL) and the emitter coupled logic (ECL), the latter used for very- high-speed systems. Take a look at some logic gates. These diagrams show various electronic switches, called gates, each of which performs a specific Boolean operation There are three basic Boolean operations, which may be used alone or in combination: 1. logical multiplication (AND gate), 2. logical addition (OR gate), and 3. logical inversion (NOT gate). The accompanying tables, called truth tables, map all of the potential input combinations against yielded outputs..... NOT/Inverter gate – (not C) AND gate – (A. B (A and B)) OR gate – (A + B (A or B or both)) NOR gate – (OR and NOT gates (not A or B or both)) NAND gate – (AND and OR gates (not A and B)) XOR/Inequality Comparator gate – (OR, AND and NAND gates (A or B but not both (A OR B but NOT (A AND B))) XNOR/Equivalence gate – (XOR gate and an Inverter (not A or B but A and B/both)) CPU:3. MEMORY UNIT Memory means the ability of computer to store the data on temporary or permanent basis. Types of Memory 1. Primary Memory It is the type of computer memory which has capability to store data temporarily. It is also called volatile memory. 2. Secondary Memory It is the type of computer memory which has capability to store data on permanent basis. It is also called non-volatile memory. (SEE PREVIOUS SLIDES) 67 PRIMARY/MAIN MEMORY The main memory of the computer, also known as the primary memory, is like a predefined working place, where it temporarily keeps information and data to facilitate its performance. When the task is performed, it clears its memory and memory space and is then available for the next task to be performed. When the power is switched off, everything stored in the memory gets erased and cannot be recalled. There are two kinds of primary (main) memory which are as follows: 1.Random Access Memory (RAM) PRIMARY MEMORY: RAM and ROM There are two kinds of Memory 1. RAM –Random Access Memory (MM) – This is used for storing programs that are currently running and data that is being processed. 2. ROM –Read Only Memory – Its contents are PERMANENTLY etched into the memory chip at the manufacturing stage. It is used – for example – to load the bootstrap loader (the program that loads as soon as you start the machine) RAM – Random Access memory Stores info about applications that are open and data VOLATILE – When you switch off the machine, it disappears!!! TYPES OF RAM DRAM - Dynamic Random Access Memory SRAM - Static Random Access Memory SDRAM - Synchronous dynamic RAM DDRAM - Double Data RAM SIMM - Single In-line Memory Module DIMM - Dual In-line Memory Module EDO-DRAM - Extended Data Out Dynamic RAM DDR SDRAM - Double Data Rate Synchronous Dynamic RAM FPM DRAM - Fast Page Mode Dynamic RAM RD-RAM – Rambus Dynamic RAM D-RDRAM - Direct Rambus Dynamic Random Access Memory MDRAM – Multibank Dynamic Random Access Memory BEDO-DRAM – Burst Extended Data Out Dynamic RAM DDR-DRAM – Double Data Rate Direct RAM ROM – Read Only Memory Non-Volatile (does not change) Programs that are necessary for the computer to run like the Boot up program (BIOS) KINDS OF ROM PROM (Programmable Read Only Memory) only one time EPROM (ELECTRONICALLY (erasable) Programmable Read Only Memory) Two or three time EEPROM (Electronic Erasable Programmable Read Only Memory) Flash Memory again and again PRIMARY/MAIN MEMORY The program currently being executed and the data used by the program is held in MAIN MEMORY MM is divided into millions of individually addressable storage units called BYTES One byte can hold one character Or one byte can hold a code representing something –i.e a part of a picture, or a sound, or a program instruction. The total number of bytes in MM = The computers MEMORY SIZE. Computer Memory Sizes 1 KB =1024 Bytes 1 MB =1024 KB 1 GB =1024 MB 1Tb =1024 GB (about 1 trillion bytes) 1 Petabyte =1024 TB 1 Exabyte =1024 PB PRIMARY/MAIN MEMORY Processing power and Main Memory in a computer has increased exponentially in the past year! It has grown at a rate that no one could have predicted. 1980 –Microcomputers with 32K of memory were bought for thousands of homes and schools! Bill Gates made the famous remark… “640 K ought to be enough for anybody..” 1981…. Things have changed drastically! 2004 –PC with 512 MB of MM was standard…. Computer Structure Processor Architecture / Fabrication / Operation Hardware (in Computer) has to do with the equipments involved in the proper functioning of a computer. Computer hardware consists of the components that can be physically handled. The function of these components is typically divided into three main categories: input, output, and storage. Components in these categories connect to microprocessors, specifically, the computer’s central processing unit (CPU), the electronic circuitry that provides the computational ability and control of the computer, via wires or circuitry called a bus. Computer System A typical computer system consists of a central processing unit (CPU), input devices, storage devices, and output devices. The CPU consists of an arithmetic/logic unit, registers, control section, and internal bus. The arithmetic/logic unit carries out arithmetical and logical operations. The registers store data and keep track of operations. The control unit regulates and controls various operations. The internal bus connects the units of the CPU with each other and with external components of the system. For most computers, the principal input devices are a keyboard and a mouse. Storage devices include hard disks, CD-ROM drives, and random access memory (RAM) chips. Output devices that display data include monitors and printers..... Software, on the other hand, is the set of instructions a computer uses to manipulate data, such as a word- processing program or a video game. These programs are usually stored and transferred via the computer's hardware to and from the CPU. Software also governs how the hardware is utilized; for example, how information is retrieved from a storage device. The interaction between the input and output hardware is controlled by software called the Basic Input Output System software (BIOS). Although microprocessors are still technically considered to be hardware, portions of their function are also associated with computer software. Since microprocessors have both hardware and software aspects they are therefore often referred to as firmware. The Computer Chipset The various components of a computer communicate with each other through a chipset, which is a collection of microprocessors connected to each other through a series of wires (also called Buses). Shown here is a diagram of a typical chipset, displaying the computer’s components and how they are connected to each other. ` COMPUTER PROCESSING METHODS Batch Processing Batch Processing (on microcomputers) the running of a batch file—a stored “batch” of operating-system commands carried out one after the other without user intervention; (on larger computers), the process of acquiring programs and data sets from users, running them one or a few at a time, and then providing the results to the users. Type of computer program processing: a mode of computer operation in which programs are executed without the user being able to influence processing while it is in progress Batch processing can also refer to the process of storing transactions for a period of time before they are posted to a master file, typically in a separate operation undertaken at night. A batch system is one which in it, the information is usually retrieved on a sequential basis, which means that the computer system read through all the records in its database, processing and updating those records for which there is some activity. COMPUTER PROCESSING METHODS 1. BATCH PROCESSING This is a technique inherited from the traditional method of mass production or assembling line production method. In computer processing environment, batch processes involves accumulating jobs or programs. Until some pre- determined time or volume is reached, the jobs may now be sorted and divided into various batches of files. The jobs in a batch will now be processed by the computer. During the processing of the job by the computer, the owner does not have access to the job at all. Interaction with the job is not feasible until the job is completed. COMPUTER PROCESSING METHODS: BATCH PROCESSING Upon completion, the results can be printed upon the computer and collected by the various owners. In order to determine which resources a job requires more correctly, the owner of the job must submit along with the job, some job – controlled information (i.e. computation time, storage space, storage medium, priority number, etc.) FEATURES OF A BPS 1. SCHEDULING POLICY: This must be in place to determine the order in which the job is processed (i.e. job – controlled information may include the priority number to determine the order of processing). In a batch, jobs may be C.P.M: BPS – FEATURES 2. IN A ROUND – ROBIN: Getting equal attention from the CPU (i.e. giving a time slice to each job) NB: The last two policies are embedded in the operating system (O. S.)that is available in the computer 3. Batch processing system has a large storage media 4. It is ideal for applications that involves large I/O amount of computations e.g. numerical computations. 5. It is ideal for most data processing applications C.P.M: BPS – DEMERITS, MERITS DEMERITS OF A BPS Inadequate control of the system Turn – around time of the system is very high BPS can be very expensive MERITS OF A BPS They can process large amount of computations (i.e. they are ideal for works like numerical computations) High amount of storage space e.g. terabytes COMPUTER PROCESSING METHODS Real Time Processing Immediacy of data processing: The time in which a computer system processes and updates data as soon as it is received from some external source such as an air-traffic control or antilock brake system. The time available to receive the data, process it, and respond to the external process is dictated by the time constraints imposed by the process. A real-time system may be defined as one which controls an environment by receiving data, processing them, and returning the results sufficiently quickly to affect the environment at that time. COMPUTER PROCESSING METHODS 2. REAL – TIME PROCESSING SYSTEM This is a system that must satisfy the requirements of producing the desired results immediately or at a particular time. They process data so quickly that the results of the processes are available to influence activities that are currently taking place. Examples include, air – line ticket reservation systems, low level entry billing systems, and so on. C.P.M: RTPS – MERITS Real – Time processing systems require fast direct access to storage devices and efficient communication network. Many users can process on a RTPS at the same time. MERITS OF RTPS Turnaround time is low Data in the database, and others used in computations reflect the most up – to – date values. For example, in an air – line booking system, a customer can apply to make a reservation online or any booking office. Before a space can be reserved, there must be seats available according to the customer’s specification, at that particular time the request is made. C.P.M: RTPS – DEMERITS DEMERITS OF RTPS No control over the system System downtime is associated with a huge lost of revenue COMPUTER PROCESSING METHODS Time Sharing Processing System simultaneous computer use: a technique for the concurrent use of a computer by many people working at remote terminals, each apparently operating as the only user of the computer's resources. The apparent simultaneous use is possible because the computer's processing speed is extremely fast in comparison with a person's typing speed at a keyboard. COMPUTER PROCESSING METHODS 3. TIME – SHARING PROCESSING SYSTEMS This is a system whereby lots of users have access to a computer system at the same time. The users are sharing the computer’s time and other resources at the same time. A TSPS has many user – terminals like that of a bank, connected to the same computer. Using this terminals, multiple users can simultaneously work on the system as can be seen from the figure on the next slide. The users are connected to the computer through an interface, over a communication network (modem, channel). The network consists of communication lines, modems, multiplexers and so on. CPM: TIME SHARING SYSTEM COMPUTER COMPUTER COMPUTER. PERIPHERAL PERIPHERAL PERIPHERAL MANAGEME CENTRAL NT PROCESSING CONSOLE UNIT MODEM MULTIPLEXER CHANNEL MODEM MODEM MODEM TERMIN TERMINA TERMINA AL L L USER 1 USER 2 USER 3 CPM: TIME SHARING SYSTEM The communication lines transmit data in an analog format, and modems converts the analog information to digital information, vice versa, to and fro terminals and channels. The channels help to route information between the terminals and computers. It should be noted that even though, all the users appear to be using the computer at the same time, the actual position is that, the CPU shifts from one user to another, spending a fraction of a second (i.e. the CPU time is allocated to all the users in a round–robin manner) CPM: TSPS – MERITS, DEMERITS MERITS OF TSPS Users have access to their job System response to users requests is usually in a matter of seconds DEMERITS OF TSPS It is expensive When the system unit fails, it fails completely and totally MULTIPLEXERS A multiplexer is a device for sending several data streams down a communications line and for splitting a received multiple stream into components. It selects one of several analog or digital input signals and forwards the selected input into a single line. They are also referred to as MUX or DATA SELECTOR. An electronic MUX can also be considered as a multiple input, single output switch. A multiplexer is often used with a complementary DEMULTIPLEXER on the receiving end and it does the exact opposite job of the MULTIPLEXER MULTIPLEXERS Definition: A digital multiplexer (MUX), is a logic circuit device that accepts I0 serial digital data input and select one of them at any given time to I1 Z pass on to the output. Outpu The multiplexer’s circuit is typically t used to combine two or more digital signals into a single line, by placing them there at different times. Technically, this is known as time- IN MUX division multiplexing. Input S is the addressing input, that controls SELECT which of the two data inputs, I0 or I1, OR CONTROL INPUT will be transmitted to the output. CODE BLOCK DIAGRAM OF A MULTIPLEXER A Mux consists of a group of data inputs and a group of control inputs. The control inputs are used to select exactly one data input to be outputted. They are also referred to as Selection Lines. The number of control inputs is directly related to the maximum number of data inputs that can be selected. A Mux with n control inputs can select from a maximum of 2^n data inputs. When n = 2, there are 2^2 = 4 data inputs that can be selected. When n = 3, there are 2^3 = 8 data inputs that can be selected. In other words, Mux has many input lines and one output line. The information on a selected input line is transferred to the output line when the device is enabled. This is a “data selector” in that it selects a data source and transfers its data to the output. The TTL 74150 selects one out of 16 data sources; the TTL 74151 selects one of 8. the TTL 74153 is a dual 4 X 1 line multiplexer that can route 2-bit data from one of four sources to a 2-bit bus MULTIPLEXERS If the S input switches back and forth at a frequency more than double the frequency of either the digital signal, both signals will be accurately reproduced, and can be separated again by a demultiplexer circuit synchronized to the multiplexer. The select or control input code determines which input is transmitted to the output Z. In the diagram below, output Z will equal data input I0, for some particular select input code or Z can also equal to I1, for another value of select input code, and so on. Thus, a multiplexer selects one (1) out of N input data sources, I1 1 and transmit the selected data to a single output I0 2 channel. This is called MULTIPLEXING. S A TWO – INPUT A 4 – INPUT MULTIPLEXER (A 4 TO 1 MUX) D0 D1 TRUTH Y TABLE A B Y D2 0 0 D0 0 1 D1 D3 1 0 D2 1 1 D3 MULTIPLEXER ICS VDD A I3 I2 I1 I0 Q Outpu 16 15 14 13 12 11 10 9 t 4539B 1 2 3 4 5 6 7 8 B I3 I2 I1 I0 Q VSS (Voltage Input) Outpu t An example of a 4 to 1 IC multiplexer is the CMOS- 4539B, and its low power Schottky TTL equivalent is the 74LS153. The IC has two multiplexers (i.e. two 4- input multiplexers combined) with its own enabled input EN mainly kept low, but both halves share the same input A and B. Other multiplexers include: The 8 to 1 (Eight input to one output) = 4512B and 74LS151 The 2 to 1 = 4019B and 74LS157 Schottky effect A reduction in the energy needed to remove an electron from a solid surface caused by the application of an electric field Electron removal from a solid surface aided by the application of an electric field MULTIPLEXING Multiplexing in computer science, is a technique used in communications and input/output operations for transmitting a number of separate signals simultaneously over a single channel or line. It is also known as multiple signal transmission. I.e., the sending of two or more signals along one communication channel. To maintain the integrity of each signal on the channel, multiplexing can separate the signals by time, space, or frequency. TYPES OF MULTIPLEXING There various types of multiplexing: 1. Space Division Multiplexing 2. Time Division Multiplexing 3. Frequency Division Multiplexing 4. Code Division Multiplexing 5. Wavelength or Dense Wavelength Division Multiplexing 6. Statistical Multiplexing 7. Orbital Angular Momentum Multiplexing 8. Polarization Division Multiplexing 9. Inverse Multiplexer Space Division Multiplexing In wired communication, space division multiplexing simply implies different point – to – point wires for different channels. Examples include an analogue stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multipair telephone cable. Wired space division multiplexing is typically not considered multiplexing and in wireless communication, space-division multiplexing is achieved by the use of multiple antenna elements, forming a phased array antenna. Examples include Multiple Input and Multiple Output (MIMO), SIMO, and MISO multiplexing. It’s a multiplexing technique in which physical separation of transmitting (antennas) is used to deliver simultaneously different data streams. SDM technique is an approach to MIMO systems and it improves capacity by increasing the number of antennas in the fading channel When we want to transmit multiple messages, the goal is maximum reuse of the given resources: time and frequency. Time-Division Multiplexing (TDM), operates by dividing the time up into time slices, so that the available time can be reused. Frequency-Division Multiplexing (FDM), operates by dividing up the frequency into transmission bands, so that the frequency spectrum can be reused. However, with directional antennas, we can actually reuse both time and frequency, by transmitting our information along parallel channels. This is known as Space-Division Multiplexing SDM is implemented through the use of Multiple Fiber arrays, Multicore Fibers (MCF), Multimode Fibers (MMF) and Few Mode Fibers (FMF) to increase the available bandwidth. Time Division Multiplexing In a Time Division Multiplexer, each sender is given exclusive access to the medium for a specific period of time. The multiple signals are carried over the same channel in alternating time slots. That is, they alternate between all possible inputs at precise time intervals. By taking turns in this manner, many inputs can share one output. Time Division Multiplexing works by the multiplexer collecting and storing the incoming transmissions from all of the slow lines connected to it and allocating a time slice on the fast link to each in turn. The messages are sent down the high speed link one after the other. Each transmission when received can be separated according to the time slice allocated. Theoretically, the available speed of the fast link should at least be equal to the total of all of the slow speeds coming into the multiplexer so that its maximum capacity is not exceeded. TDM Continues... Two ways of implementing TDM are: 1. Synchronous TDM 2. Asynchronous TDM The Synchronous TDM works by the multiplexer giving exactly the same amount of time to each device connected to it. This time slice is allocated even if a device has nothing to transmit. This is wasteful as there will be many times when allocated time slots are not being used. This does not guarantee maximum line usage and efficiency. With the Asynchronous TDM, the length of time allocated is not fixed for each device but time is given to devices that have data to transmit. It tags each frame with an identification number to note which device it belongs to and this may require more processing by the multiplexer and take longer but time saved by efficient and effective bandwidth utilization makes it worthwhile. It therefore allows more devices than there is physical bandwidth for. This type of TDM is used in Asynchronous Transfer Mode (ATM) networks Frequency Division Multiplexing In a Frequency Division Multiplexer, data from multiple nodes is sent over multiple frequencies, or channels, over a network medium. The carrier bandwidth is divided into sub-channels of different frequency width, each carrying a signal at the same time in parallel. For FDM to work properly, frequency overlap must be avoided. The link must have sufficient bandwidth to be able to carry the wide range of frequencies required. The Demux at the receiving end works by dividing the signals by tuning into the appropriate frequency. FDM operates in a similar way to radio broadcasting where a number of different stations will broadcast simultaneously but on different frequencies. Listeners can then “tune” their radio so that it captures the frequency or station they want. FDM gives a total bandwidth greater than the combined bandwidth of the signals to be transmitted. In order to prevent signal overlap, there are strips of frequency that separate the signals. These are called Guard Bands. A common example of FDM use is Cable Television (CATV) which can be achieved with coaxial cable or fiber-optic cable. A multiplexer is used to combine many channels to maximize the use of the available bandwidth and a demultiplexer built into the television or set top box (decoder) will separate the channel that the viewer wants to watch Code Division Multiplexing Code Division Multiplexers have since found their ways into modern cellular networks in the form of Code Division Multiple Access (CDMA). They are semiconductor devices that work by assigning each input a unique complex mathematical code, similar to but more advanced than those developed during World War II for cryptographic purposes. Each input applies its code to the signal it receives, and all signals are simultaneously sent to the output. At the receiving end, a Demultiplexer performs the inverse mathematical operation to extract the original signals. Spectrum Technology is the transmission of data over a wide range of frequencies. In wireless networks, the available frequency spectrum for data transmission is limited, and simultaneous transmission over the same frequency is a possibility with a growing number of users. Each transmission is coded with a unique code that can be decoded only by the specified network device that receives the transmission. Wavelength or Dense Wavelength Division Multiplexing This is used in Optical Fiber Communications, to increase bandwidth over existing fiber optic backbones, with each transmission using different wavelength of light and thereby making multiple transmissions of signals simultaneously over the same communication channel. It muxes a number of optical carrier signals into a single optical fiber signal by using different wavelengths (i.e. colors) of laser light. With light, different frequencies correspond to different colors. Several transmissions can be sent over the same fiber by using different light colors and combining into a single light stream. Statistical Multiplexing This form of multiplexing uses statistical techniques to dynamically allocate transmission space depending on the traffic pattern in the transmission channel. It is a type of communication link sharing strategy, whereby the communication channel is been divided into an arbitrary number of variable bit-rate digital channels or data streams. The link sharing is adapted to the instantaneous traffic demands of the variable data streams that are transferred over each channel in comparison to the fixed sharing of a link, as in the case of TDM and FDM Allocation of time slot to users is on First – Come – First – Served basis. Users messages are queued in a buffer and the buffers empty into time slots as soon as slots become available on the shared medium. Any user can be assigned to any time slot at any time. Statistical Multiplexing is facilitated through packet – oriented communication, which is been used in packet switched computer networks, where each stream is divided Orbital Angular Momentum Multiplexing It is a relatively new experimental technique for multiplexing multiple channels of signals, carried using electromagnetic radiation over a single path. It muxes signals carried on electromagnetic waves using the OAM of the waves to differentiate between the various orthogonal signals. It can potentially be used in addition to Polarization Division Multiplexing This technique uses the polarization of electromagnetic radiation to separate orthogonal channels. It is a physical layer method for multiplexing signals carried on electromagnetic waves. It is in practical use in both radio and optical communications, particularly in 100GBit/s per channel fibre optic transmission systems. INVERSE MULTIPLEXER Also known as imux, it allows a high speed link or a data stream to be broken into multiple lower speed or data rate communication links. It differs from a demultiplexer because the multiple output streams stay inter- related, whereas, that of a demultiplexer are unrelated. DEMULTIPLEXER This provides the reverse operation of a multiplexer, since they allow a single input to be routed through to one of n outputs selected via m-control lines (n = 2m). If there are 8 outputs = 3m control lines. The circuit element is usually referred to as a 1 – to – n demultiplexer. The circuit consists basically of n AND gates, one for each of the 2m possible combination of m control input, with the single line fed to all these gates. Since only one AND gate will ever be active, this determines which output the input is fed to. Block diagram of 1 – to – n Demux. A B Control inputs Y0 Y1 X 1 – of – n Demux Yn Circuit diagram of 1 – of – 4 _ _ Demux A A B B X A B X Y N 0 0 X Y 0 0 1 X Y 1 1 0 X Y 2 1 1 X Y 3 Truth table 1 – of – 4 Demultiplexer APPLICATION OF MUX / DEMUX PARALLEL TO SERIAL DATA CONVERSION Note that many digital systems process binary data in parallel format (all bits simultaneously) because it is faster. When data is to be transmitted over relatively long distance however, the parallel arrangement is undesirable because it requires a large amount of transmission line: this is with a huge cost. For this reason, binary data or information in parallel form is often converted into serial form before being transmitted to a remote distance. One method of performing this parallel – series conversion is by using a MUX. The data are presented to the input of the multiplexer with the appropriate select code and a clocking sequence, the output maybe all the input one after the other in a serial form. To convert the data back to parallel format, a demultiplexer can be used. Data communication between 2 computers over a long distance 1 to n to COMPUTER n COMPUTER 1 Dem SYSTEM Mux SYSTEM ux Location 1 Location 2 MODEMS The term “MODEM” is derived from Modulator/DEModulator, which describes the device’s basic function. A modem is a device that modulates (or converts) the binary data generated by the computer into Analog waves that can be sent over the phone lines; at the end of the telephone line, a second modem demodulates the Analog signal back to digital data and relays it back to another computer. Some modems can transmit data at a speed of about 56kbps. These are referred to as 56k modems. MODEMS Modems are available in two basic forms: Internal and External modems. Internal modems. They take the form of expansion card that plug into a PC’s ISA (Industry Standard Architecture) or PCI (Peripheral Component Interface/ Interconnection) bus slot. The following are the merits and demerits: MERITS DEMERITS 1. No extra power supply 1. It is more difficult to install needed because it requires opening the whole system unit to plug in. 2. It is slightly cheaper than 2. It is difficult to monitor: external modems. Internal modems don’t have exposed LEDs to expose their operations. MODEMS External modems. External modems are separate unit that you connect to a computer’s serial port with a cable and you also connect it to a telephone line. MERITS DEMERITS 1. It is easy to monitor i.e. 1. It is slightly more the speaker and the LEDs on expensive that an external modem enables internal modems. you to see what is happening at that moment. 2. It is easy to install 2. It requires an external power supply source. MODEM device connecting computers via phone line: an electronic device that connects computers via a telephone line, allowing the exchange of information. It consists of a modulator to convert computer information into a telephone signal and a demodulator to convert it back again. MODEM... Modem, device that enables computers, facsimile machines, and other equipment to communicate with each other across telephone lines or over cable television network cables. In the strictest sense, a modem is a device that converts between analog signals, such as sound waves, and digital signals, which are used by computers. However, the term has also come to include devices that permit the transmission of entirely digital signals. MODEM... Modems transmit data at different speeds, measured by the number of bits of data they send per second (bps). A 28.8 Kbps modem sends data at 28,800 bits per second. A 56 Kbps modem is twice as fast, sending and receiving data at a rate of 56,000 bits per second. Analog MODEMS An analog modem converts the digital signals of the sending computer to analog signals that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer. A standard analog modem has a maximum speed of 33.6 Kbps. Analog MODEMS... The word modem is an acronym formed from the two basic functions of an analog modem: modulation and demodulation. To convert a digital signal to an analog one, the modem generates a carrier wave and modulates, or adjusts, it according to the digital signal. The kind of modulation used depends on the application and the speed of operation for which the modem is designed. For example, many high-speed modems use a combination of amplitude modulation, in which the amplitude of the carrier wave is changed to encode the digital information, and phase modulation, in which the phase of the carrier wave is changed to encode the digital information. The process of receiving the analog signal and converting it back to a digital signal is called demodulation. INTEGRATED SERVICES DIGITAL NETWORK Instead of converting between analog telephone lines and digital applications, Integrated Services Digital Network (ISDN) carries digital signals throughout the transmission process. Because an ISDN modem does not convert between digital and analog signals, it does not perform the modulation and demodulation functions from which modems derived their name. An ISDN modem simply processes the digital signal between the computer and the ISDN lines. INTEGRATED SERVICES DIGITAL NETWORK... ISDN transmission lines are ordinary two- wire telephone lines that carry digital signals on three separate channels. The telephone company uses one channel for tracking and control purposes; the remaining two channels can be used to transmit voice, data, or both. Digital data bypasses the analog voice network, enabling it to travel much faster. ISDN has a maximum speed of 128 Kbps. ASYMMETRICAL DIGITAL SUBSCRIBER LINE Like ISDN, Asymmetrical Digital Subscriber Line (ADSL) permits the transmission of digital data over ordinary telephone lines. It is called asymmetrical because it transmits data in one direction (from the network) faster than it does in the other direction (to the network). ADSL carries signals to the network at speeds of up to 640 Kbps, and it can deliver data from the network at speeds of up to 8.1 million bits per second (Mbps). ASYMMETRICAL DIGITAL SUBSCRIBER LINE... An ADSL modem splits an ordinary telephone line into three separate data channels, each with different capacities and speeds. The lowest-capacity channel transmits analog voice data; a second, medium- capacity channel transmits data to the network; and the highest-capacity channel transmits data from the network. ASYMMETRICAL DIGITAL SUBSCRIBER LINE... A number of other forms of DSL are also available, depending on the speed of data transmission and the distance of the customer from the central office. These include High-Data-Rate Digital Subscriber Line (HDSL), Very-High-Data Rate Digital Subscriber Line (VDSL), and Symmetric Digital Subscriber Line (SDSL). CABLE MODEM Cable modems permit the transmission of data over community antenna television (CATV) networks—that is, the network of cables used to distribute cable television. A cable modem transmits data from the network at about 3 Mbps and transmits data to the network at between 500 Kbps and 2.5 Mbps. CABLE MODEM... Like a standard analog modem, a cable modem converts between a digital signal and an analog signal. Cable modems are much more complex than standard analog modems. They also incorporate a tuner that separates the digital data from the rest of the broadcast television signal. Because users in multiple locations share the same cable, the modem also includes hardware that permits multiple connections and an encryption/decryption device that prevents data from being intercepted by another user or being sent to the wrong place. DAC Digital-to-Analog Converter or DAC, device for converting digital data into current or voltage analogs. DACs are now widely used in compact disc (CD) players, in digital audio- and videotape players, and in digital signal processing audio and video equipment. Most DACs use some form of resistor (Resistor, component of an electric circuit that resists the flow of direct or alternating electric current. Resistors can limit or divide the current, reduce the voltage, protect an electric circuit, or provide large amounts of heat or light) network. Digital data is applied to the resistors in groups of bits. The resistances vary in definite ratios; the current flow in each one relates directly to the binary value of the bit received DIGITAL → ANALOG CONVERSION (DAC) A digital quantity has a value that is specified as one or two quantities i.e. it can only take 1 or 2 quantities. An Analog quantity can take on any value over a continuous range of value. How? Digital to Analog conversion is the process of taking a value represented in digital codes (Binary) and converting it into a voltage or current equivalent to the digital value. The diagram shows a typical 4-bit D/A Converter. Vref = 16 volts D MSB C D/A VOUT B Converter DAC Analog out A LSB A block diagram of a D/A Converter D C B A VOUT Their is an input for a 0 0 0 0 0 voltage reference. This 0 0 0 1 1 input is used to 0 0 1 0 2 determine the maximum 0 0 1 1 3 value that the D/A can 0 1 0 0 4 produce. 0 1 0 1 5 The input ABCD are 0 1 1 0 6 digital values or binary 0 1 1 1 7 bits derived from a 1 0 0 0 8 1 0 0 1 9 register of a digital 1 0 1 0 10 system. 1 0 1 1 11 The Analog output, Vout is 1 1 0 0 12 equal in volt to the binary 1 1 0 1 13 number 1 1 1 0 14 1 1 1 1 15 The output can also be twice the binary number from the diagram or some other proportionality factors i.e. Analog Output = K x Digital Input Where K = Proportionality factor (constant for a given DAC). So, the Analog Output can be a current or voltage; for a current, the unit of K is in Ampere and Volt for voltage output. For example. 1. A 5-bits DAC has a current output for a digital input of 10100, and output current of 10 mAmp is produced. What will be I out for a digital input of 11101? Solution: The digital input 101002 = 20 Therefore, because Iout = 10 mA 10 mA = K. 20 K = 0.5 mA. What will be the Iout when input is 111012 = 29. Therefore Iout = 0.5 x 29 = 14.5 mA DIGITAL → ANALOG CONVERSION (DAC) E.g. 2. What is the largest value of output voltage from an 8-bit DAC that produces 1.0 v for digital input of 001100102 = 50? Solution: Analog output = K x Digital input 1.0v = K x 50 K = 0.02v = 20 mV. What is the largest output? This is when all the bits are high i.e. when everything occurs as 1 i.e. 111111112 = 255 Vout(Max) = 20 mV x 255 = 5.10 Volts Resolution of a D/A Converter ADC Analog-To-Digital Converter or ADC, an electronic device for converting data from analog to digital form for use in electronic equipment such as digital computers, digital audio and video recorders, and communication equipment. Analog or continuously varying electrical waveforms are applied to the device and are sampled at a fixed rate. Sample values are then expressed as a digital number, using a binary numbering system consisting only of 0's and 1's. The resulting digital codes can be used in various types of communications systems. Analog → Digital Conversion The Analog to digital converter takes an Analog signal and produces a digital output code which represents the equivalence of the Analog signal. VA cloc k VDA Block Diagram of an A/D Converter The block diagram shows an Analog to digital converter (a close approximation). The aim is to get the exact digital output, and its basic operation depends on the difference between two Analog signals being compared with the digital output of the converter. Its operation also involves a D/A Converter. The control unit has three inputs which are: 1. Output from the voltage comparator 2. A clock, and 3. A start command. The voltage comparator compares two Analog signals and its output to the control unit depends on which Analog signal is greater. Operation of the A/D Converter 1. When the start command gives high, the A/D conversion process starts. 2. The clock determines the rate at which data are sent by the control unit to the register. 3. The register holds a binary number which is passed unto the D/A Converter. The output of the D/A Converter is an Analog signal which is applied to the comparator. 4. The input signal to the A/D converter is also fed into the comparator (i.e. the Analog signal we are trying to convert is also passed unto the comparator). Let the input Analog be VA and the output from the D/A be VDA (i.e. Let Input Analog = VA and Output from D/A = VDA. 5. i. If VDA is less than VA, the comparator’s output is High. (if VDA < VA = HIGH) ii. When VDA = VA; the comparator’s output goes LOW iii. When VDA is slightly greater than VA, the comparator’s output is LOW. If the comparator’s output is LOW, the comparator stops the process of modifying the binary number stored in the register. This is likely to occur when the VDA is approximately equal to VA. At this stage, the digital number in the register is also the digital equivalence of the input signal VA. 6. If the comparator’s output is HIGH, the comparator will continue to modify the content of the register until the comparator goes LOW again. Example: An A/D converter has a clock frequency of 1MHz. The fullscale output of the D/A converter is 8.190 volts, with a 12-bit input. The comparator’s threshold voltage is 1 mVolt. If VA = 4.528 volts, determine: a. The digital number obtained from the register b. The D/A converter’s % resolution. SYSTEM VIABILITY Viability is the ability of a thing (a living organism, an artificial system, an idea, etc.) to maintain itself or recover its potentialities. A viable system is any system organised in such a way as to meet the demands of surviving in the changing environment. One of the prime features of systems that survive is that they are adaptable. ATTRIBUTES OF SYSTEM VIABILITY 1.RELIABILITY: Reliability is a broad term that focuses on the ability of a product to perform it’s intended function. It can be defined as the probability that an item will continue to perform it’s intended function without failure for a specified period of time under stated conditions. Please note that the product defined here could be an electronic or hardware product, a software product, a manufacturing process or even a service 2.PRODUCT AVAILABLITY: Product availability is the probability that a product will be available at any instance required. It is a measure of the degree to which a product is in an operable and committable state at the start of a mission, when the mission is called for at an unknown random time. Product Availability can be expressed mathematically as: Availability = MTBF/(MTBF + MTTR) Where MTBF is Mean Time Between Failures and MTTR is Mean Time To Repair Mean time between failures (MTBF) This is the predicted elapsed time between inherent failures of a system during operation. It can be calculated as the arithmetic mean (average) time between failures of a system A measurement of error occurrences that can be tracked over time to indicate the quality of a system The MTBF is typically part of a model that assumes the failed system is immediately repaired (MTTR), as a part of a renewal process. This is in contrast to the mean time to failure (MTTF), which measures average time to failures with the modelling assumption that the failed system is not repaired (infinite repair time). Mean time between failures (MTBF) describes the expected time between two failures for a repairable system, while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system. MTBF = (∑(Start of downtime – Start of uptime))/number of failures For example, three identical systems starting to function properly at time 0 are working until all of them fail. The first system failed at 100 hours, the second failed at 120 hours and the third failed at 130 hours. The MTBF of the system is the average of the three failure times, which is 116.667 hours. If the systems are non-repairable, then their MTTF would be 116.667 hours. The definition of MTBF depends on the definition of what is considered a system failure. For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair. Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures in this context. In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure. Mean Time To Repair (MTTR) This is a basic measure of the maintainability of repairable items. It represents the average time required to repair a failed component or device Expressed mathematically, it is the total corrective maintenance time for failures divided by the total number of corrective maintenance actions for failures during a given period of time. It generally does not include lead time for parts not readily available or other Administrative or Logistic Downtime 3.PRODUCT DEPENDABILITY: Product Dependability is a measure of the degree to which a product is operable and capable of independent functions at any random time. It is a combination of reliability and availability. 4.PRODUCT QUALITY: Product quality is the totality of expression of the consumers/customers showing satisfaction in the performance of a product after a long experience and use of the product.

Computer Hardware Systems Study 1 COSC 319 PDF

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