How Computers WorkPart 318 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 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

Alphanumeric Text

8-bit ASCII sample0 0101 00001 0101 00012 0101 0010

A 0100 0001B 0100 0010C 0100 0011

0100100001100101

011011000110110001101111

Hello

Hello

How are pictures stored?

MonochromeA pixel can look BLACK,or it can look WHITE.

ASCII Images Instead of pixels, use characters Web site that converts pictures

http://asciiconvert.com/ An example

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:

000 001 010 011 100 101 110 111

Mixes various amounts of R G and B light to produce other colors.

Color

Or a pixel display various colors

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

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)

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

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

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

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

Introduces new opportunities People assume they know who owns the site

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)

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