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CSCI 51 Introduction to Computer Science

CSCI 51 Introduction to Computer Science. Dr. Joshua Stough January 22, 2009. Last Time in CSCI 51. Syllabus Sakai Eclipse Hello_World, SimpleIO_Demo. Today in CSCI 51. Parts of the computer hardware vs. software CPU and memory Binary numbers What is an algorithm?

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CSCI 51 Introduction to Computer Science

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  1. CSCI 51Introduction to Computer Science Dr. Joshua Stough January 22, 2009

  2. Last Time in CSCI 51 • Syllabus • Sakai • Eclipse • Hello_World, SimpleIO_Demo

  3. Today in CSCI 51 • Parts of the computer • hardware vs. software • CPU and memory • Binary numbers • What is an algorithm? • Book references: Chapters 1 and 2, wiki computer

  4. Before Programming... • You need a basic understanding of how a computer works • if you’re going to drive a car, you need to know that it runs on gasoline... • Understanding the pieces will help you understand what your programs actually do • Plus, we want you to be able to talk intelligently about computers

  5. Hardware vs. Software A computer is made up of hardware and software Software Hardware • CPU • ex: 1.8 GHz Core 2 Duo • input/output • keyboard • 15.4” wide screen LCD • network card • main memory • ex: 2 GB RAM • secondary memory • ex: 160 GB hard drive • operating systems • Windows XP • Mac OS X • applications • games • Microsoft Word • Mozilla Firefox

  6. Hardware Organization CPU memory motherboard hard drive

  7. Central Processing UnitCPU • Control Unit (CU) • "the brain" of the CPU • Program Counter (PC) • points to the next instruction to be executed • Instruction Register (IR) • holds the currently executing instruction • Arithmetic Logic Unit (ALU) • carries out all arithmetic and logical ops • Accumulator (ACC) • holds the results of the operations performed by the ALU

  8. Main Memory • Ordered sequence of cells • AKA Random Access Memory (RAM) • Directly connected to the CPU • All programs must be brought into main memory before execution • When power is turned off, everything in main memory is lost

  9. Main MemoryWith 100 Cells Each memory cell has a numeric address, which uniquely identifies it

  10. CPU and Main Memory All programs must be brought into main memory before execution Chip that executes program instructions Primary storage area for programs and data that are in active use (RAM)

  11. Secondary Storage • Provides permanent storage for information • Retains information even when power is off • Examples of secondary storage: • Hard Disks • Floppy Disks • ZIP Disks • CD-ROMs, DVDs • Tapes

  12. Secondary Storage Secondary memory devices provide long-term storage Information is moved between main memory and secondary memory as needed

  13. Input Devices • Definition: devices that feed data and computer programs into computers • Examples: • Keyboard • Mouse • Secondary Storage

  14. Output Devices • Definition: devices that the computer uses to display results • Examples: • Printer • Monitor • Secondary Storage

  15. Input/Output Devices I/O devices facilitateuser interaction

  16. Hardware Components

  17. Opening Notepad • Use the mouse to select Notepad • The CPU requests the Notepad application • Notepad is loaded from the hard drive to main memory • The CPU reads instructions from main memory and executes them one at a time • Notepad is displayed on your monitor

  18. Questions • - points to the next instruction to be executed • - a unique location in memory • - stores information permanently • Instructions executed by the CPU must be first loaded into

  19. Software Categories • Operating System • controls all machine activities • provides the user interface to the computer • first program to load when a computer is turned on • manages computer resources, such as the CPU, memory, and hard drive • examples: Windows Vista/XP, Linux, Mac OS • Application • generic term for any other kind of software • examples: word processors, missile control systems, games

  20. Operating System (OS) • OS monitors overall activity of the computer and provides services • Written using programming language • Example services: • memory management • input/output • storage management

  21. Application Programs • Written using programming languages • Perform a specific task • Run by the OS • Example programs: • Word Processors • Spreadsheets • Games

  22. Questions Classify the following pieces of software as operating system or application: • Microsoft Windows XP • Microsoft PowerPoint • Linux • Your CSCI 51 programs

  23. It’s All About Data • Software is data • numbers, characters • instructions, programs • Hardware stores and processes data • read, write • add, subtract, multiply, divide

  24. Analog vs. Digital • Analog • continuous wave forms • ex: sound, music on an audio tape • Digital • the information is broken down into pieces, and each piece is represented separately • represented as series of 0 and 1 • 0 - low voltage • 1 - high voltage • can be copied exactly • ex: music on a compact disc

  25. Representing Text Digitally • All information in a computer is digitized, broken down and represented as numbers. H i , H e a t h e r . 72 105 44 32 72 101 97 116 104 101 114 46 Corresponding upper and lower case letters are separate characters.

  26. ASCII Character Codes

  27. Language of a Computer • Machine language: the most basic language of a computer • A sequence of 0s and 1s • binary digit, or bit • sequence of 8 bits is called a byte • Every computer directly understands its own machine language • why can't Windows programs run on Apple computers?

  28. 1 bit 2 bits 3 bits 4 bits 0 1 00 01 10 11 000 001 010 011 100 101 110 111 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111 Bit Permutations Each additional bit doubles the number of possible permutations

  29. 1 bit ? 2 bits ? 3 bits ? 4 bits ? 5 bits ? How many items can be represented by Bit Permutations • Each permutation can represent a particular item • There are 2N permutations of N bits • N bits are needed to represent 2N unique items 21 = 2 items 22 = 4 items 23 = 8 items 24 = 16 items 25 = 32 items

  30. Binary Numbers • N bits to represent 2N values • N bits represent values 0 to 2N-1 • Example: 5 bits • 32 unique values (0-31) • 00000 = 0 • 11111 = 31 24 23 22 21 20 16 + 8 + 4 + 2 + 1

  31. Decimal to Binary 114 1110010 Number Place Value Digit 114 26 = 64 1 50 25 = 32 1 18 24 = 16 1 2 23 = 8 0 2 22 = 4 0 2 21 = 2 1 0 20 = 1 0

  32. QuestionsBinary Numbers • What’s the maximum value a 6-bit number can represent? • What’s the decimal representation of 111010? • What’s the binary representation of 35? 63 58 = 32+16+8+2 100011

  33. Storage Capacity • Every memory device has a storage capacity, indicating the number of bytes (8 bits) it can hold • Various units: Unit Symbol Number of Bytes KB 210 = 1024 kilobyte megabyte gigabyte terabyte MB 220 (over 1 million) GB 230 (over 1 billion) TB 240 (over 1 trillion)

  34. Questions • - computer components including the CPU, main memory, I/O devices, and secondary storage • - the brain of the computer, containing the CU, PC, IR, ALU, and ACC • - computer instructions to solve a problem • The digits 0 and 1 are called or the shortened term

  35. Programming LanguagesEvolution • Early computer programmers programmed in machine language (only 0s and 1s) • Assembly languages were developed to make programmer’s job easier • Assembler: translates assembly language instructions into machine language

  36. Assembly and Machine Language

  37. Programming LanguagesEvolution • High-level languagesmake programming easier • Closer to spoken languages • Examples: • Basic • FORTRAN • COBOL • C/C++ • Java

  38. From Java to Machine Language • Computers understand only 0 and 1 (machine language) • Compiler translates source code into machine code • Java compiler translates source code (file ending in .java) into bytecode (file ending in .class) • bytecode is portable (not machine-specific) • Java interpreter reads and executes bytecode • different Java interpreters for different types of CPUs and operating systems (OS) • Intel/Windows, Motorola/Mac OS X, Intel/Linux

  39. Problem Solving • The purpose of writing a program is to have the computer solve a problem • But: • “Computers do not solve problems; they implement solutions.” – Laurent Gasser • The general steps in problem solving are: • understand the problem • dissect the problem into manageable pieces • design a solution • consider alternatives to the solution and refine it • implement the solution • test the solution and fix any problems that exist

  40. Algorithm • Sequence of instructions used to carry out a task or solve a problem • May be written in either English or pseudocode • outline of a program that could be translated into actual code • May need refinement as you work Always write/think out your algorithm before you begin programming

  41. Problem-Analysis-Coding-Execution most important step without computer with computer

  42. Algorithm Design Example Problem: Convert change in cents to number of half-dollars, quarters, dimes, nickels, and pennies to be returned. Example: • given 646 cents • number of half-dollars: divide 646 by 50 • quotient is 12 (number of half-dollars) • remainder is 46 (change left over) • number of quarters: divide 46 by 25 • quotient is 1 (number of quarters) • remainder is 21 (change left over) • number of dimes, nickels, pennies • result: 12 half-dollars, 1 quarter, 2 dimes, 0 nickels, 1 penny

  43. Resulting Algorithm • Get the change in cents • Find the number of half-dollars • Calculate the remaining change • Find the number of quarters • Calculate the remaining change • Find the number of dimes • Calculate the remaining change • Find the number of nickels • Calculate the remaining change • The remaining change is the number of pennies.

  44. 6 Fundamental Concepts of Programming • Variables, and Assignment (data storage) • Expressions, and Data Retrieval • Conditional statements (making choices) • Loops (repetition) • Structured data, arrays (data abstraction) • Functions (procedural abstraction)

  45. Problem Set 1 • Temp • Time • Money • WireTransfer • Make sure programs compile and runs • Due Monday Feb 2 at 11:59pm

  46. What’s Ahead... • More Java Basics • Reading: Ch 2 and 3

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