1. How Computers Work Part 3 18 February 2008

2. 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

3. 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

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

5. 01001000 01100101 01101100 01101111 H e l l o Hello

6. How are pictures stored?

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

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

9. 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:

10. 000 001010011 100101110 111

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

12. The Internet  What is it? The infrastructure that connects identified computers Links = the wires Routers = the boxes that connect them  World Wide Web Computers that contain information to be shared Servers

13. How Do You Get to the Servers?  Computers are connected through a network  Network requires protocol to work A protocol is a set of rules The one that is used here is called IP (Internet Protocol)

14. How would you route a note?  Assume that you each have a consecutive number (count off)  If I hand one of you a note for a set number, what do you need to know?  Which way to go – not exactly where it is  Your number, the number you want to get to  Algorithm?  If number is greater, pass left/back smaller, pass right/forward equal, read

15. How Networking Works  Computers need the same thing Who identified by IP address  Every machine that is connected to the network has one  http://www.lawrencegoetz.com/programs/ipinfo/ http://www.lawrencegoetz.com/programs/ipinfo/  Command prompt Routers know how to get there

16. So What Can Go Wrong in Transit?  Data can be read  Data can be lost  Data can be changed  Data can be sent to someone else

17. How Networking Works  Computers need the same thing Who identified by IP address  Every machine that is connected to the network has one  http://www.lawrencegoetz.com/programs/ipinfo/ http://www.lawrencegoetz.com/programs/ipinfo/  Command prompt Routers know how to get there  But IP addresses aren’t user friendly Give names instead Domain Name Server does the mapping

18. Introduces new opportunities  People assume they know who owns the site

19. Anatomy of a URL  Protocol: server-name/file-to-display  Protocol: usually http Have you ever seen others? https?  Server-name The computer’s name  Usually begins with www  Usually ends with 3 characters that define the kind of site However, there are no rules: as long as its registered, you can get there  File-to-display Can be a whole path (just like Windows)

20. How to Build that File  Text file that says what to display Web pages use HTML Hypertext Markup Language  Two types of information Text Instructions on how to display