Lecture notes
CompSci Computer Systems (Year 11/GCSE/Nat 5)
Complete class notes of computer science computer systems course with in depth explainations, diagrams, and exam tips.
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COMPSCIComputer Systems
Data Representation
Binary-term to describe data stored and processedby digital systems like computers, transmitted as a series of on
and off electrical pulses.
Why?
- Simplicity - messages sent by simplifying turing transistor on and off to allow electricity to pass
- Storage - data can be stored easily as it only needs on and offs
- Signal degradation - binary is resistance to electrical drops in voltage due to resistance as the value will not
change
1 bit = 1 binary digit (1)
1 byte = 8 binary digits (10011011)
Denary 128 64 32 16 8 4 2 1
=55
Binary 0 0 1 1 0 1 1 1
Floating Point Representation -a way to store realnumbers in a form of scientific notation
0. 164 × 1
0
2
10100100 10
The mantissa - digits that make up the number - 164
Mantissa Exponent
The base - number that it is multiplied by - 10
he digits that
T he number of places to
T
The exponent - the power that defines how many times to multiply by - 2
make up the move the digits
Can also be written in base 2 (binary) number
10
0. 10100100 × 2
The binary point will always be left of number, and base is always 2 thus negating the need to store the “x2”
ASCII- American Standard Code for Information Interchange.
Computers use binary numbers to store characters that make up text, punctuation, and symbols. The oldest
standard system is ASCII. It uses 7 bits of binary to define 128 characters. Extended ASCII covers 8 bits which
allows more symbols.
First 32 characters (0-31) are non-printable characters and are used to control peripherals or send signals to devices.
(e.g. Backspace, Cancel, New line)
“Hi” -> 72 105 -> 01000110 01100111
Current standard is called UNICODE that uses 16 bits (650000) characters to represent symbols.
79
, Vector Graphics -a series of instructions describingshapes and lines to produce images. Not for real-world scenes
as they are too complex to break down into a list of objects and attributes. Used commonly for icon design,
simplistic drawings, or flowcharts and graphs.
Objects:
- Rectangles
- Ellipses
- Polygons
- Lines
Attributes:
- Coordinates
- Line colour
- Fill colour
SVG (Scalable Vector Graphics) are how vector graphics are produced on webpages.
Rectangle :<rectx="50"y="20"width="100"height="80"
style
="
fill
:
b
lue
;
s
troke-width
:
3
;
s
troke
:
red
"
/>
Rectis the name of the object, a rectangle
x=”50” y=”20”
are the coordinates of the top leftcorner. These are given from left and top margin of SVG area
in pixels
width=”100” height=”80”define width and height ofrectangle
Attributes containing fill colour and line colour are in thestyleproperty.
Ellipse:<ellipsecx="250"cy="170"rx="100"ry="50"
style
="
fill
:
r
ed
;
s
troke
:
purple
;
stroke-width
:
5
"
/>
rx=”100” ry=”50”they define the radius from centrepoint along the x and y axis (if same value, make circle)
cx=”250” cy=”170”are coordinates of the centre ofthe ellipse
Line:<linex1="200"y1="20"x2="450"y2="160"style="stroke:black"/>
x1=”200 y1=”20”gives the start of the line coordinates
x2=”450” y2=”160”gives the end of the line coordinates
Polygon:<polygonpoints="250,250 450,450 50,450"
style
="
fill
:
y
ellow
;
stroke
:
black
;
stroke-width
:
10
"
/>
points=”250,250 450,450 50,450”defines the coordinatesof the corners of the shape in x,y pairs. Three pairs
create a triangle
80
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