Data Representation

Question 1

What are natural numbers

Answer 1

numbers used for counting and ordering including 0

Question 2

what is an integer

Answer 2

any positive or negative whole number

Question 3

what is a rational number

Answer 3

includes numbers that can be expressed as a fraction or ratio

Question 4

what is irrational number

Answer 4

a number which cannot be expressed exactly as a fraction

Question 5

what is a real number

Answer 5

a number that is either rational or irrational is considered a real number

Question 6

what is an ordinal number

Answer 6

a number usef to show the position of which a value appears such as 3rd 4th 5th

Question 7

benefits of using hexadeciamal ?

Answer 7

• much easier to read and remember than a string of binary
• quicker to write ortype since hex takes up only one character not four
• there is a less change of making an error when typing hex
• used to define colours, used in MAC, in assembly languages and machine code
• easy to convert to and from binary

Question 8

what is two’s complement and the method?

Answer 8

it is a method to represent negative values in binary by representing the MSB as -128

Find -x in binary

• find the value of x in binary
• flip the bits of x in binary
  
  • add 1 to the result

Question 9

what is fixed point binary

Answer 9

binary value uses a specified number of bits where the placement of the binary point is fixed

Question 10

The common prefixes used to represent bytes

Answer 10

Question 11

Uncommon, more accurate prefixes to represent bytes

Answer 11

Question 12

What is ASCII

Answer 12

a way of represnting each character on a keyboard as a binary value.

Question 13

what is Unicode

Answer 13

was introduced to standardise the encoding of chracters from all languages.

Question 14

what is a transmission error

Answer 14

when data doesnt always arrive in the same format it was sent, due to -

• electrical interference
• power surges
• synchronisation issues

these cause bits to flip and data to be corrupted

Question 15

what are the four methods of error detection

Answer 15

• parity bits
• majority voting
  
  • check digits
    
    • checksums

Question 16

How is a parity bit used for error detection

Answer 16

• the parity bit is set at the transmittieng end and parity is checked at the recieving end
• if the wrong number of bits are on, an error has occured
  
  • the recieving computer requests the data

Question 17

how is majority voting used for error detection

Answer 17

• each bit of a message is sent three times
  
  • if a bit value is flipped the recipient computer uses the majority rule and assumes the other two bits have not changed

Question 18

how are checkdigits used for error detection

Answer 18

• check digit is an additional digit at the end of a string to check for mistakes in input or transmission
• ISBN or EAN
  
  • the 13th digit is calculated by an algorithm called modulo 10

Question 19

How is a checksum used for error detection

Answer 19

• total sum of all bytes in transmission of data is calculated using an algorithm
• the sum is often sent with the data
• receieving computer recalculates the checksum and compares
  
  • if they do not match the data is requested

Question 20

what are bitmapped graphics, common forms?

Answer 20

when a grid of pixels are created and each pixel is given a colour value

• JPG
• GIF
  
  • PNG

Question 21

what is colour depth

Answer 21

• a pixel is attributed a number of n bits
• the number of combinations dictates the bit depth and therefore the number of colours that can be represented
  
  • a higher bit depth gives a greater range of colour and a better image quality

Question 22

what is the image file size determined by?

Answer 22

the number of pixels used and the number of colour combinations available

Question 23

what is metadata

Answer 23

it is data about data and is stored in the same file as the image data this includes

• the date of creation
• resolution
• colour deth
  
  • gps co-ordinates of wherea a photo was taken

Question 24

what is metadata

Answer 24

it is data about data and is stored in the same file as the image data this includes

• the date of creation
• resolution
• colour deth
  
  • gps co-ordinates of wherea a photo was taken

Question 25

define analogue data

Answer 25

data that is infinitley variable and is often represented in the form of a wave

Question 26

define digital data

Answer 26

often represented as discrtete values with on and off whown as set peaks and troughs

Question 27

What is sampling

Answer 27

the process of converting analogue sound waves into digital form to create digital sound.

Question 28

the process of analogue to digital conversion

Answer 28

* analogue sound samples are recorded via an amplifier * each sample is quantised to measure its wave height and translate this into an integer value * the integer value is then converted and stored as binary

Question 29

what is sample resolution

Answer 29

number of bits used to record each measurement , more bits used per sample enables the height of the wave to be more accuratley measured

Question 30

How do you calculate the file size of a sound file

Answer 30

file size = sample rate x resolution x length

Question 30

How do you calculate the file size of a sound file

Answer 30

file size = sample rate x resolution x length

Question 31

what is Nyquist's theorem

Answer 31

because sound is made up of many components at different frequencies samples must be twice the highest frequency in order to replicate the original sound wave

Question 32

define compression

Answer 32

the process of encoding information with fewer bits so that the files take less memory

Question 33

define lossy data compression

Answer 33

non-essential data is permanently removed e.g. different shades of same colour, or frequencies outside human hearing range

Question 34

define lossless data compression

Answer 34

patterns in the data are identified and summarised in a shorter format without permanently removing any information

Question 35

what is run length encoding

Answer 35

a basic method of compression that summarises consecutive patterns of the same data

Question 36

what is dictionary compression

Answer 36

spots regularly occuring data and stores it in a seperate dictionary.

Question 37

define encryption

Answer 37

a way of making sure data cannot be understood if you dont possess the means to decrypt it.

Question 38

describe the process of encryption

Answer 38

* plaintext of a message sent is encrypted using a cipher algorithm and key into equivalent ciphertext * when recieved, the ciphertext is decrypted back into plaintext

Question 39

describe the vernam cipher

Answer 39

a one time pad is used to encrypt the text, it must be equal to or longer than in length than the original text and must be truly random. the pad must be shared by hand and destroyed after use