How Computers Work Part 1 18 September 2006

Sometimes They Don’t Having a Bad Day Mouse Won’t Work

What does a Computer Do Well?  Intelligence amplifier amplifies our ability to perform mental activities “power tools” for the mind Can process much more information  Does repetitive tasks quickly and correctly Check things more quickly Removes people from boring tasks  Manipulates forms and data

What Wasn’t Possible Before?  We can do things in virtual environmentsvirtual environments  Chemists can see things at microscopic levelsmicroscopic levels Micron: millionth of a meter  Model weatherweather  Hurricane predictions  Model historic eventshistoric events

Marvelous Manipulator  Manipulates form, not content Everything is a symbol Computers do not understand meaning  When it appears to understand or apply judgment… Reflecting human knowledge that is encapsulated Programming: capturing our knowledge “expert systems”  Examples from movies or books?

What a Computer Does  One input, one output Displaying a movie  One input, multiple outputs Different reports from the same data  Multiple inputs, one output Computing a statistic  Other examples? IN PROCESS OUT

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

What is an algorithm?  A detailed sequence of actions to perform to accomplish some task  Named after an Iranian mathematician, Al- Khawarizmi 813 – 833 C.E. Mathematician: algebra, trigonometry, geometry Astronomy and geography as well

Examples of Algorithms  Mapquest directions  Assembly instructions  User’s manual  Software program  Other examples?

A simple algorithm  Using a calculator, how do you find the average of three numbers? Assume no average function Assume that the calculator is already on  Solution Enter the first number; enter + Enter the second number; enter + Enter the third number; enter / 3 =

A bigger example  Using a calculator, how do you find the average of 100 numbers? No longer want to list one by one  Introduces loops  Solution For each number, Enter the number; enter + Enter / 100 =

A more complex algorithm  Take the absolute value of a number  Introduces decision making  Solution If the number is less than 0 The answer is –number Else The answer is number

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