6 September How Computers Work

Follow Ups VeriSign: : A Space Odyssey Produced in 1968 as science fiction Intel founded Sony introduces Trinitron technology Keyboard, mouse & windows demonstrated First “artificial intelligence” program Apollo Guidance Computer Tentacle Arm

Computer in the Arts About the work When was the work written or produced? What’s the genre? The role of computers A character or a tool? Central to the plot or peripheral? How computers are portrayed Intelligent or simplistic? Threatening, helpful or neutral?

Current Event: Hurricane Images Google Earth: gives people a view of the world Google Earth "I am trying to get a current overlay for the area around 2203 Curcor Court in Gulfport, Miss." grass-roots effort identified scores of post-hurricane images from NOAA determined landmarks to integrate into Google Earth posted them By Saturday, Google, NASA, CMU formalized Power of the Internet: everyone can contribute This is a great use of Google Earth Are there bad ones? NY Times, Sept 5

To Understand … How your web page works How does a computer work? How do web pages work? How you share your web page What is a network? What is the Internet?

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

Exercise Break into 3 groups Devise an algorithm to order a group of people from shortest to tallest We will then execute it on another group

Homework Assignment A triangle is a 3-sided figure. The sum of any 2 sides must be longer than the third side. Write an algorithm to check if three numbers could constitute the sides of a triangle. It produces a result of “yes” or “no”. (This is also a dry run to make sure that blackboard is working properly.)

Simplified Model of a Computer processor instructionsdata the information that it works on defines an algorithm retrieves the instruction directs data movement

Data A computer doesn’t work on actual numbers, but locations (called variables ) Does action to whatever value is in that location Variables that have values that never change are constants Demonstration How would you swap two numbers? Why do computers work like this?

Data Types All data is stored as a series of zeroes and ones Computer doesn’t know if it is numeric or text or what format it is Computer assumes that the instructions know the format of the data

Programming Languages Ways to describe algorithms Lots of ways to describe, but a machine has only one way to execute A program translates the language the person writes into something the computer understands Compilers translate once, interpreters translate every time Later in the semester we’ll look at what the computer understands

Web Pages Web pages are defined in a language called HTML (HyperText Markup Language) Hypertext: text that has different paths that can be taken Markup Language: the text that is to be presented and instructions (markups) on how to present it

Hypertext Proposed by Vannevar Bush in 1945 We do not think or learn linearly We need to understand many concepts and how they come together People have different knowledge and learning skills We want to go off and further explore ideas In literature, we may want to explore alternative outcomes

Markup Language Source does not appear the way that it will eventually look Contrast: WYSIWYG -- What You See Is What You Get Advantage: easy to edit Disadvantage: hard to visualize

Editting HTML files Two options Edit HTML Use a WYSIWYG Why learn HTML? Tool to understand computers Why use HTML? Control Simple changes