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 ID: 475980
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Slide1
Information in ComputersSlide2
Remember
Computers
Execute algorithms
Need to be told what to do
And to whom to do itSlide3
Question
How does the computer know what to act on?Slide4
Answer
We tell it
WHERE
NOT WHATSlide5
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!]Slide6
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!]Slide7
What can be stored in a computer?
Instructions
Numbers
Text
Pictures
Audio
VideoSlide8
How is it stored?
1s and 0s
“bits is bits”
The same series of 0s and 1s can mean different things!
Question of interpretation!Slide9
NumbersSlide10
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 systemSlide11
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 valuesSlide12
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-FSlide13
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?Slide14
How to represent fractions
How to represent 1/3?
.3
.33
.333
Representation can change the result!
What is easy in decimal, may not be easy in binary!
[embezzlers can take advantage of rounding issues!]Slide15
TextSlide16
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 0100 0001
B
0100
0010
a
0110 0001
b 0110 0010
[Can you guess why some alphabetizing puts ALL capitals before lowercase?]Slide17
Storing Strings
When do they end?
Known length
Give length
Signal end
Signaling the end is the most common waySlide18
ImagesSlide19
Black and White PicturesSlide20
Pictures are stored as pixels
Monochrome:
BLACK or WHITESlide21
What is needed?
Different levels of black and white
Shades of gray
Percentage of blackSlide22
ASCII Images (
picascii.com
)
Instead of pixels, use charactersSlide23
C
o
l
o
r
P
i
c
t
u
r
e
sSlide24
Color?????
But all I can store is 1s and 0s!
Let’s see how we can represent colors!Slide25
ColorsSlide26
Colors – Paint
(Subtractive Color Model)
Primaries: magenta, yellow, and cyan
T
his
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.Slide27
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.Slide28
Colors (
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#)
E
ach
color is indicated by a number from 0-255
(0,0,0) = black
(255,255,255) = whiteSlide29
Color PicturesSlide30
What is a Color Pixel?
Red Green and Blue
Each has a value from 0 to 255Slide31
FormatsSlide32
Many Formats
j
peg 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 sizesSlide33
VideoSlide34
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 realitySlide35
AudioSlide36
Sampling
Like video,
sample it fast enough and we can fool the ear
But what is that is sampled?Slide37
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)Slide38
HomeworkSlide39
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 TuesdaySlide40
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 instructionsSlide41
Chrome
Everything we do should work on all browsers
BUT it works differently
We therefore REQUIRE that you use ChromeSlide42
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