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Computer basics and i.o devices

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  • ALU. ALU performs the actual operations through the use of electronic signals. This unit is capable of electronic signals. This unit is capable of performing automatically addition, subtraction, multiplication, division, comparing, selecting, and other mathematical and logical operation. What happens I the ALU while an instruction is being executed? In most computers only one word at a time can be transferred between the ALU and the memory. Hence, to perform an operation involving two arguments, the first argument moat be transferred from the memory to the ALU and stored there temporally while the second argument is being transferred. The special memory cell it the ALU for this purpose is called the accumulator. The operation being performed, the result is formed in the accumulator before it is transmitted back to memory.
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  • The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU).
    CPU is perhaps the most influential component. It has two functions:(1) it obtains instructions from the memory and interprets them and (2) it performs the actual operations. The first function is executed by the control unit which in its turn also performs two functions. It(1) interprets the instruction and, on the basis of this interpretation,(2) tells the ALU what to do next.
    Early CPUs were composed of many separate components but since the mid-190s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
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  • A computer is an electronic machine which can accept data in a certain form, Process the data, and give the results of the processing in a specified format as information.
    A computer system consist of two parts: hardware and software. Hardware is any electronic or mechanical part you can see or touch. Software is a set of instructions, called a program, which tells the computer what to do.
    A general purpose computer has four main sections: the arithmetics and logic unit(ALU), the control unit, the memory, and the input and output devices(collectively termed I/O). there parts are interconnected by busses, often made of groups of wires.
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  • In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally.
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Transcript

  • 1. Today’s Class
    • Course overview
    • Introduction to Computer Systems
      • What is both Computer and Computer Science?
      • Components of a Computer System
      • Computer Hardware
      • Fetch-Decode-Execute Cycle
      • Computer Software
  • 2. Computer and Computer Science: Definition
    • A computer is an electronic device, which can input, process, and output data.
    input processing output
    • A computer Science is the discipline that seeks to build a scientific foundation for such topics as computer design, computer programming, information processing, and algorithmic solutions of problems.
    • A computer is a machine that stores data, interact with devices, and execute programs (provides computing capabilities to its users).
  • 3. Major Components of a Computer System
    • A computer system consists of two main parts: hardware and software.
    • Hardware is the electronic and mechanical parts of a computer system.
    • Software is the data and the computer programs of a computer system.
  • 4. Computer Hardware Basic hardware components
    • Computer hardware is divided into three major Components:
      • 1.  The Central Processing Unit (CPU)
      • 2. Computer memory
      • 3. Input/Output (I/O) devices   
  • 5. CPU
    • The CPU is the " brain " of the computer system.
      • It does the fundamental computing within the system
      • It directly or indirectly controls all the other components
    • The CPU has a limited storage capacity . It relies on memory to hold data and programs and to save results.
    • The CPU consists of:
      • 1.      The Arithmetic and Logic Unit (ALU).
      • 2.      The Control Unit (CU).
      • 3.      Registers.
    • The CPU components are connected by a group of electrical wires called the CPU bus .
  • 6. CPU PC: Program Counter Register MAR: Memory Address Register MDR: Memory Data Register
    • The CPU is connected to memory and I/O devices by the System bus
    • The System bus consists of: Address-, Control- and Data-buses.
  • 7. Computer Memory
    • The main function of computer memory is to store software .
    • Computer memory is divided into primary memory and secondary memory.
    • Primary memory is divided into random access memory (RAM) and read-only memory (ROM) :
        • RAM holds the programs and data that the processor is actively working with.
        • ROM contains software that is used in Input/Output operations. It also contains software that loads the Operating System in Primary Memory.
        • The CPU can read and write to RAM but it can only read from ROM.
        • RAM is volatile while ROM is not.
    • Secondary memory is used for long-term storage of programs and data.
      • Examples of secondary memory devices are: hard disks, floppy disks and CD ROMs.
  • 8. Primary Memory
    • Primary memory is divided into a number of memory cells (bits) or bytes.
    • A bit (binary digit) is the smallest storage unit within a computer. It is a tiny electrical circuit that can be in one of two states:
      • A voltage high represented by the symbol 1
      • A voltage low represented by the symbol 0
    • Any system of symbols can be represented by bit or byte patterns.
    • Each byte has a unique integer address and it is usually 8 bits.
  • 9. Primary Memory 1,099,511,627,776 40 2 TB Terabyte 1,073,741,824 30 2 GB Gigabyte 1,048,576 20 2 MB Megabyte 1,024 10 2 KB Kilobyte 1 0 2 Byte Number of bytes POWER OF 2 SYMBOL UNIT
  • 10. Primary and Secondary Memory Comparison Slow Cheap Large capacity Not connected directly to the processor Fast Expensive Low capacity Connects directly to the processor Secondary memory Primary memory
  • 11. I/O (Input/Output)Devices
    • Input devices are used to enter programs and data into a computer.
      • Examples : keyboard, mouse, microphone, scanner, and bar code reader.
    • Output devices are where program output is shown or is sent.
      • Examples : monitor, printer, and speaker.
    • An I/O device is directly connected to the System, but through a device controller.
  • 12. Fetch Decode Execute Cycle
    • The CPU continuously transfers data to and from the primary memory
    • Data transfer is done in units called instructions or words
    • When a computer is switched on, the CPU continuously goes through a process called fetch-decode-execute cycle :
      • The Control Unit fetches the current instruction from memory, decodes it and instructs the ALU (Arithmetic Logic Unit) to execute the instruction.
      • The execution of an instruction may generate further data fetches from memory
      • The result of executing an instruction is stored in either a register or RAM
  • 13. Fetch-Decode-Execute Cycle (cont’d) Main Memory Control Unit Arithmetic/Logic Unit 1 2 3 4 Instruction Cycle Execution Cycle Fetch Decode Execute Store cpu RAM
  • 14. Computing Environments Personal computing Time-sharing Distributed computing
  • 15. Software
    • Software is the programs and data that a computer uses.
      • Programs are lists of instructions for the processor
      • Data can be any information that a program needs: character data, numerical data, image data, audio data, etc.
      • Both programs and data are saved in computer memory in the same way.
    • Computer software is divided into two main categories:
      • 1. Systems software
      • 2. Applications software
    • System software manages computer resources and makes computers easy to use.
    • An applications software enables a computer to be used to do a particular task.
  • 16. Computer Software Types of software Software
  • 17. Software   Operating system. Networking system. Programming language software. Web site server. Data backup.
    • Word processors
    • Game programs
    • Spreadsheets
    • Data base systems
    • Graphics programs
    • Web browsers
    Systems Programs Application Programs
  • 18. Operating Systems
    • The most important systems program is the operating system.
      • It is a group of programs that coordinates the operation of all the hardware and software components of the computer system.
      • It is responsible for starting application programs running and finding the resources that they need.
    • Examples of operating systems are: Unix, Windows NT, Windows XP, MS-DOS, Linux, Solaris, VMS, OS/2 and System 7.
  • 19. Computer Languages Computer language evolution The only language understood by a computer is machine language. Note:
  • 20. Writing, Editing, Compiling, and Linking Programs typical Java environment Primary Memory . . . . . . Disk Disk Disk Editor Compiler Class Loader Program is created in an editor and stored on disk in a file ending with .java . Compiler creates bytecodes and stores them on disk in a file ending with .class . Class loader reads .class files containing bytecodes from disk and puts those bytecodes in memory. Phase 1 Phase 2 Phase 3 Primary Memory . . . . . . Bytecode Verifier Bytecode verifier confirms that all bytecodes are valid and do not violate Java’s security restrictions. Phase 4 Primary Memory . . . . . . Interpreter Interpreter reads bytecodes and translates them into a language that the computer can understand, possibly storing data values as the program executes. Phase 5
  • 21. Program Execution Executing programs
  • 22. System Development Model Figure 1-12 System development model An old programming proverb: Resist the temptation to code. Note: Pseudocode A precise algorithmic description of program logic. Note: