# Systems Overview by fjhuangjun

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• pg 1
```									Representing Information

Semester 1, Week 2, Lect 1
Types of Information
How many groups of „types of information‟ can
you make from the following?
   A chess board diagram.
   A satellite photograph.
   A computer program.
   The value of ∏ (PI) to 100,000 decimal places.
   A set of directions to a particular street.
   A recording of bird-calls.

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Types of Information (2)
 Five types of information the computer
commonly manipulates:
   Numeric (we‟ll talk about it later)
   Character
   Visual (Graphic)
   Audio
   Instructional
First, the information must be transformed (converted)
into an acceptable representation that the
computer will accept.
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What is Information to a Computer?
 A computer functions on electricity and
magnetism. The magnetism is very
often a product of electrical flow.

 There is a great deal of light and
reflection in modern hardware (lasers
and fibre optics) but light is a medium
generated by electrical flow.

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What is Information to a Computer? (2)
 Electricity in a computer circuit has
voltages (DC - direct current):
 @ +12 Volt for a disk drive,
 @ + or -5 Volt or + or -3 Volt for
buses and communications wiring,
 @ 1.5 or 1.3 Volt for the processor.
(Now 1.7?)

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What is Information to a Computer? (3)
 Whatever the voltage the flow can be
switched on and off - or be present or
absent.
 Voltage on might equal a 1,
 Voltage off might equal a 0. Binary!

 All information (instructions, data, etc.)
flows through the hardware system as
'Power On' or 'Power Off„ - as 1s and 0s.
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Binary Numbers
 All modern computers work with a
system of numbers that are binary
numbers.

 The two symbols: 0 and 1.

 Each is called a „bit‟, short for 'binary
digit„.
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Binary Numbers (2)
 Binary circuits: Electronic devices are
cheapest and function most reliably if
they assume only two states.

Open                        Closed
circuit                     circuit

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Representation of Symbols and Text
 To store any kind of information in the
computer‟s memory, it must first be
transformed into a binary numeric form.
 Symbols and Text
 Includes characters, punctuation,
symbols representing numbers.
 Each symbol can be assigned a
numeric value.

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Representation of Symbols and Text (2)
 Two standardized sets of codes for
symbols:
 ASCII: American Standard Code for
Information Interchange (128
characters. 00000002 to 11111112.
256 characters in extended ASCII,
000000002 to 111111112)
 EBCDIC: Extended Binary Coded
Decimal Interchange Code.

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Representation of Symbols and Text (3)
A partial listing of the ASCII-to-binary
character set:
Ctrl+@    0000000
Ctrl+A    0000001
Ctrl+B    0000010
Ctrl+C    0000011
Ctrl+D    0000100
Ctrl+E    0000101
Ctrl+F    0000110
Ctrl+G    0000111
Space     0100000
Delete    1111111
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0   0110000
1   0110001
2   0110010
3   0110011
4   0110100
5   0110101
6   0110110
7   0110111
8   0111000
9   0111001
:   0111010
.   1011110
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A   1000001
B   1000010
C   1000011
D   1000100
E   1000101
F   1000110
G   1000111
H   1001000
I   1001001
J   1001010
K   1001011

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Representation of Symbols and Text (4)
 The message “Hello.” in Binary

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Representation of Symbols and Text (5)
 Try decoding the following:

1010100   1001000           1001001          1010011
0100000   1001001           1010011          0100000
1000001   0100000           1010011          1010100
1010101   1010000           1001001          1000100
0100000   1010000           1010010          1001111
1000010   1001100           1000101          1001101
0100001

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Representation of Images
 Pictures:
 A picture must be transformed into
numeric form before it can be stored
or manipulated by the computer.
 Each picture is subdivided into a grid
of squares called pixels (picture
elements).

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Representation of Images (2)

 An image on paper can be converted
into pixels using a scanner.
 Digital cameras store their images as
digital images, i.e. the picture is
memory as pixels.

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Representation of Images (3)

A picture with only black and white pixels:
1 represents black.
0 represents white.

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Representation of Images (4)
010101010101010101010110101101001001000111110000
011010101010101010101001011010010110010100000110
100101010101010101010110110001010000101001010100
101101101011011010110101100110010110100010001001
011010010110100101101010001001100100101101010010
100101101100101011010101110110011001010010101100
011010010011010110010010001001100110101010010001
010101101100101100100101110110011001010100100101
010101010101010011011010001001100010100001010100
101010101010101100010010110010001101001110100001
010101010101010001000101000101101000010000001101

=          110110101010010100110100011010010011100101101000
101001010100100010100101100101101100001010000010
101011010001001001001001011110101011010100101100
101010000100010010010111110101111100101001001001
010100101001000100101010101110101011010010010000
101001000010011001101111101011101010101000100101
010010010100100011011000011110111011010110101000
000100000001001100100111111111110110111000000010
101000101010010011011000010101011101000010101000
000010000100101101010011111111111111011101000101
001000101001101010100100011101111110100010010000
010010010110001001001001111011110101101100100101
100100100000111010010010010111111111011001001000

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Representation of Images (5)
 Photographic quality images have a
gray-scale.
white are used.

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Representation of Images (6)
 4 level gray-scale
used.
Each pixel needs 2 bits:
00   -   represents   white
01   -   represents   light gray
10   -   represents   dark gray
11   -   represents   black

This picture has 4 levels of gray
(this uses four bits).

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Representation of Images (7)
 256 level gray-scale
means
8 bits per pixel are needed

This picture has 256 levels of gray
(this uses eight bits).

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Representation of Images (8)
 We could also use 8 bits
(known as a byte) to
represent the colour of a
pixel.
 A byte can represent 256
different numbers, so we
can have 256 different
colours in the image.

This picture uses 256 colours.

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Graphics Colours
 Red, Green, Blue (RGB)
 The primary light colours use three
values per pixel.
 One number is used for each of the
amounts of Red, Green and Blue on the
computer screen.
Red         Green       Blue

Colour of pixel

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Representation of Images (again)

This is a full colour image.

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Image Resolution
 Image resolution is measured by the
number of pixels from left to right
across an image and the number of
pixels from top to bottom down an
image.
 More pixels = higher resolution = better
quality image.

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Image Resolution (2)
 What are two specifications/attributes
of digital cameras that indicate their
power?
 Answer: Pixel quantity and memory
capacity.
 E.G. Nikon Coolpix S640 (12.2 MPx, 45
Mb) that has over twelve million pixels
and forty-five megabytes of 'on-board'
memory.
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Representing Sound
 Representation of any sound by using
digital recording:
 The sound is divided into tiny
segments and stored as binary
numbers.
 The computer transforms these
binary numbers and reproduces the
voltages.

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Representing Sound (2)
   These voltages are
sent down the
speaker wires to
produce sound.

A sound wave represented by the sequence:

0, 1.5, 2.0, 1.5, 2.0, 3.0, 4.0, 3.0, 0 (Amps)

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Representing the Instructions of
Programs
 Instructions are described as being
imperative in the sense that they
command action - or, at least, advise
action.
 In most aspects of life:
 Instructions must be clearly
 The information needed to process
available.
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Representing the Instructions of
Programs (2)
 Examples:
 Setting a microwave oven.
 Following a cooking recipe. (Consider
that a recipe has a method
(instructions) and ingredients (data)).
 It is similar with computer programs.
Programs are all (essentially) sequential
instructions and need to be structured
with 'complete information'.
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Representing the Instructions of
Programs (3)
 A common book definition:
 Program: A collection or list of
commands designed for a computer
to follow, which gives some desired
result.
 The structure of a program instruction
is often logical and may include
mathematical principles. There may
need to be operands - also known as
data.
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Representing the Instructions of
Programs (4)
 The difference between a recipe
instruction and a program instruction is
that the recipe will still work if you vary
the method, whereas a program will
have 'bugs' if it is not sequentially
perfect.
 A computer‟s instructions must be
stored in binary form within the
computer before they can be used.

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Conclusion
 The „things‟ that a computer uses;
   Input such as data,
   That which is processed,
   Outputs
   „Feedback‟ (if used)
-   these can all be described as
information of one sort or another.
Whatever a computer is used for, its information
requires a method of representation for
manipulation and storage.
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Next…

 … Number Systems -

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