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How Computers Work

How Computers Work. Part 3 18 February 2008. 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.

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How Computers Work

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  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

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