1. 1 February How Computers Work

2. Buying Bugs A 21st Century Entrepreneurship How do you find bugs in your software? Offer a bounty! How do malicious hackers gain an advantage? Buy it! NY Times article

3. Computers as a Tool What is a tool? A device used to perform or facilitate manual or mechanical work Something regarded as necessary to the carrying out of one's occupation or profession Something used in the performance of an operation An instrument

4. Thinking about Tools Write down a favorite tool or device Write down what it is intended to do Write down an alternative use Switch with a neighbor Write down another alternative Switch back

5. Computers: The Most Adaptable of Tools Why? We can PROGRAM the computer Instructions are called software Embedded computers Programmed by the manufacturer General purpose computers Programmed by the consumer

6. How Does a Computer Work? It is actually a very simple machine It executes exactly what it is told to do Forrest Gump “Run, Forrest, run” Forrest Computers execute algorithms

7. Simplified Model of a Computer processor instructionsdata the information that it works on defines an algorithm retrieves the instruction directs data movement Control Unit Arithmetic Logic Unit MEMORY Performs the operations

8. Binary System Everyone knows that computers store bits, right? What does it mean? All data is stored as a series of zeroes and ones Why? 1 0 =

9. Representing Numbers Additive system ||||| ||||| Every item represents 1 Examples of additive systems? Positional system Value = face * place 37 = 3*10 + 7*1 ||||

10. Positional System Base = number of different values in a position Base 10 = 10 values: 0-9 Base 2 = 2 values: 0-1 Value of each position = power of base b 4 b 3 b 2 b 1 b 0 Binary: 2 4 2 3 2 2 2 1 2 0

11. Binary Positional System 1 0 = 0000 = 0010 = 8 4 2 1 = 0001 0100 = = 0011 0 1 2 3 4

12. Examples 2 4 2 3 2 2 2 1 2 0 16 8 4 2 1 Examples 1111 = 15 1000 = 8 01100100 = 100

13. Data Types Computer doesn’t know what the bits represents or what format is being used Computer assumes that the instructions know the format of the data What are the types of data? Numbers, text, pictures, sound, instructions

14. Data Types Numbers: integers and floating point numbers (scientific notation) Why do we need floating point numbers? Text: Unicode, double byte Languages and symbols (Word insert symbol) Pictures: pixels A very fine needlepoint How to represent color? Sound: different formats Instructions

15. Alphanumeric Text 8-bit ASCII sample 0 0101 0000 1 0101 0001 2 0101 0010 A 0100 0001 B 0100 0010 C 0100 0011

16. 01001000 01100101 01101100 01101111 H e l l o LOGICAL _______________ Hello

17. How are pictures stored?

18. Monochrome A pixel can look BLACK, or it can look WHITE.

19. ASCII Images Instead of pixels, use characters Web site that converte pictures http://asciiconvert.com/ An example

20. Or it can display various shades of grey: 000 001 010 011 100 101 110 111 0 1 2 3 4 5 6 7 For example:

21. 000 001010011 100101110 111

22. Mixes various amounts of R G and B light to produce other colors. ColorColor Or a pixel display various colors: