1 February How Computers Work

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

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

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

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

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

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

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 =

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

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:

Binary Positional System 1 0 = 0000 = 0010 = = = =

Examples Examples 1111 = = = 100

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

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

Alphanumeric Text 8-bit ASCII sample A B C

H e l l o LOGICAL _______________ Hello

How are pictures stored?

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

ASCII Images Instead of pixels, use characters Web site that converte pictures An example

Or it can display various shades of grey: For example:

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