How Computers Work

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

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

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

10. 100 101 110 111 001 010 011 000

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