Information in Computers

Remember Computers Execute algorithms Need to be told what to do And to whom to do it

Question How does the computer know what to act on?

Answer We tell it WHERE NOT WHAT

Implications Doesn’t know what it is acting on So, it doesn’t care if it is adding 3 to 5 or 7 million to 10 billion: Just an add! [That’s how a calculator works!]

Computer trusts you! Told it that there was a number there And you put a string there: It will treat it as a NUMBER You may not like the result [one of the ways that people hack computers!]

What can be stored in a computer? Instructions Numbers Text Pictures Audio Video

How is it stored? 1s and 0s “bits is bits” The same series of 0s and 1s can mean different things! Question of interpretation!

Numbers

Storing an integer Computer only has 2 values it can use: 0, 1 How many do we have? 0-9 So how do we represent the tenth value? Place-value system

Binary Numbers With one “bit”, I can represent just two values With two bits: 0 or 1 “twos” 0 or 1 “ones” Total of four values

Binary Numbers for People All those 0s and 1s are hard to read Group them in 4s (like credit card numbers) Then write them in decimal But WAIT! Goes to 15 Use letters A-F

Storing numbers should be easy, right? How big is a number? How do you indicate a negative number? How do you represent a fraction? Remember scientific notation? Id there an equivalence for computers? Does any of this matter to you?

How to represent fractions How to represent 1/3? Representation can change the result! What is easy in decimal, may not be easy in binary! [embezzlers can take advantage of rounding issues!]

Text

Storing Characters Also need to be converted to 0s and 1s Numerous encodings ASCII, ANSI, ISO support a single language UTF-8 (Unicode) supports all languages Examples: A B a b [Can you guess why some alphabetizing puts ALL capitals before lowercase?]

Storing Strings When do they end? Known length Give length Signal end Signaling the end is the most common way

Images

Black and White Pictures

Pictures are stored as pixels Monochrome: BLACK or WHITE

What is needed? Different levels of black and white Shades of gray Percentage of black

ASCII Images (picascii.com)picascii.com Instead of pixels, use characters

Color PicturesColor Pictures

Color????? But all I can store is 1s and 0s! Let’s see how we can represent colors!

Colors

Colors – Paint (Subtractive Color Model) Primaries: magenta, yellow, and cyan This color system is called subtractive because: each primary color absorbs (subtracts) a certain part of the color spectrum. every time a color is added, less light is reflected. When you mix all three primaries together, the entire spectrum of color is absorbed, and we’re left with black.

Colors - Lights (Additive Color System) Primaries: Red, Blue, Green Additive color systems start without light (black). Light sources combine to make a color. As colors are added, the resulting color is brighter.

Colors (colorpicker.com)colorpicker.com We’ll be working with the additive color system Mix various amounts of red, green, and blue to create a color. Colors can be represented by rgb (red#, green#, blue#) Each color is indicated by a number from (0,0,0) = black (255,255,255) = white

Color Pictures

What is a Color Pixel? Red Green and Blue Each has a value from 0 to 255

Formats

Many Formats jpeg or jpg, png, tif, gif, … Different encodings, different sizes Actually different ways to COMPRESS them Why compression? 1000 red pixels in a row… That’s why they are different sizes

Video

The picture part What is film? Series of pictures taken (and shown) close enough together to fool the eye Known as the frame rate Sampling the reality

Audio

Sampling Like video, sample it fast enough and we can fool the ear But what is that is sampled?

Digital Sound (with apologies to physics majors) Sound waves cause the air to vibrate Vibrations have frequencies (how fast they move) A specific sound can be represented by how much of each frequency it has (just like a pixel is how much of each color it has)

Homework

Filezilla We will be using these tools on Tuesday 130 people can NOT download Just download Filezilla DO NOT TRY TO SET IT UP Will discuss on Tuesday

AnyConnect If you live off campus or will be traveling, you will need AnyConnect You can only download it on campus Can NOT use it on campus We will provide instructions

Chrome Everything we do should work on all browsers BUT it works differently We therefore REQUIRE that you use Chrome

AFS access AFS is the system that the university uses to manage files You don’t need to know anything about it You DO need to have it enabled for your onyen Enabling is not instantaneous