Section 3 Data Representation

Question 1

what is a natural number ?

Answer 1

a whole number that is used for cointing

Question 2

what is a rational number?

Answer 2

any value that can be expressed as a ratio or a fraction

Question 3

what is an irrational number?

Answer 3

a number that can not be expressed as a ratio or a fraction

Question 4

what is an ordinal number ?

Answer 4

decsribes the numerical position of objects

Question 5

why are hexadecimals used ?

Answer 5

as a shorthand binary since it is simple to represent a byte in just 2 digit
they are easier to remeber compared to a 8 bit sequence

Question 6

what is a byte?

Answer 6

8 bits

Question 7

what is ASCII

Answer 7

Americamn Standard Code for Information Interchnage

a way of representing letters, numbers and symbols as binary

Question 8

what is unicode

Answer 8

a way of representing data using 16 bit binary compared to the 8 bit ascii

Question 9

what are partity bits?

Answer 9

a parity bit is an additional bit that is used to check that the other bits transmitted are likely to be correct

Question 10

what is majority voting?

Answer 10

this is a system that requires each bit to be sent 3 times. if a bit is flipped erroneously during transmission over a noisy line, the recipient computer would use the majority rule and assume that the two bits that have not chnaged were therefore correct

Question 11

what is a check digits?

Answer 11

it is an additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission.

Question 12

what are the rules for binary addition?

Answer 12

0+0 = 0
1+0 = 1
1+1 = 0 ( carry the 1)
1+1+1  = 1 ( carry the 1)

Question 13

what is an overflow ?

Answer 13

this is when the result of the addition is greater than 255, and an over flow error occurs where a carry from the most significant bit requires a ninth bit

Question 14

what is unsigned binary?

Answer 14

unisgned representation of binary can only represent positive numbers

Question 15

what is signed bianry?

Answer 15

can represent both positive and negative numbers

Question 16

how do you perform twos compliment?

Answer 16

• write out the positive intergrer in normal binary
• flip all of the bits ( turn the 1s into 0s and turn the 0s into 1s)
• add 1

example :
-5
00000101
11111010
11111011

Question 17

fixed point binary

Answer 17

0.5 = 0.1
0.25 = 0.01
0.125 = 0.001
0.0625 = 0.0001
etc

Question 18

what is a bitmap image?

Answer 18

an image that contains many picutr elements or pixels , that make up the whole image.

Question 19

what is resolution?

Answer 19

width in pixles * height in pixels

Question 20

what is resolution sometimes expressed as ?

Answer 20

PP1 = Pixels Per Inch
or
DPI = Dots Per Inch

Question 21

what is the colour depth?

Answer 21

the number of bits that determine the number of combinations

Question 22

what is metadata?

Answer 22

data about data
additional details that are stored with the image such as :
-width 
-height
-colour depth

Question 23

What are vector graphics ?

Answer 23

vector images are made up of geometric shapes / mathematical equatoions and objects such as lines , curves , arcs and polygons

Question 24

Vector Graphics vs Bitmap graphics

Answer 24

• vectors will usually have a smaller sile size
• vectors will scale perfectly
• vectors transmit and load faster

Question 25

what is the sampling rate ?

Answer 25

the frequency with which you record the amplitude of sound

how many readings u take per specific time interval

Question 26

Calculating sound sample sizes

Answer 26

number of samples per second * the number of bits per sample * the legnth of the sampe in seconds

Question 27

what is an analouge signal ?

Answer 27

a continuous signal which represents physical measurements

Question 28

what is a digital signal ?

Answer 28

discrete time signals generated by digital modulation

Question 29

examples of continuous siganls ?

Answer 29

• human voice
• tape recorder
• analouge watch

Question 30

example of digital signals ?

Answer 30

computers
cds
dvds
digital watch

Question 31

how do we quantify analouge sound

Answer 31

continuous varying quantities are measuered

Question 32

how is a digital signal quantified ?

Answer 32

quantities are counted rather than measured

Question 33

analouge to digital conversion

Answer 33

• a microphone convertsthesound energy into electrical energy
  the analouge to digital converter sampels the analouge data at a given frequency, measuring the amplitude of the wave at each point
• then converts this into a binary value according to the resolution

Question 34

what is frequency ?

Answer 34

something that us determined by the speed of oscillation or vibration of a wave

Question 35

what is nyquists theorem?

Answer 35

in order to produce an accurate recording the sampling rate msut be doubled that of the highest frequency in the original signal

Question 36

what is lossy compresion?

Answer 36

this is when non essential informtion/ data is remved

Question 37

what is loseless compression?

Answer 37

records a pattern in data. using these patterns the computer can reverse the proceduer and reassemble an image

Question 38

what is rle?

Answer 38

Run legnth encoding , records a pixles value and the number of times it repeats

Question 39

what is encryption?

Answer 39

encryption is the transformation of data from one form to another to prevent an unauthroised third party from being to be able to understand the data

Question 40

what is caeser cipher ?

Answer 40

this is a type of substitution cipher and works by shifiting the letters of the alphabet along by a given number of characters

Question 41

what is vernam cipher ?

Answer 41

implementation of a class of ciphers known as one time pad ciphers . offers perfect security if used properly