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Computer Science > Data Representation > Flashcards

Data Representation Flashcards

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1
Q

What are natural numbers

A

numbers used for counting and ordering including 0

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2
Q

what is an integer

A

any positive or negative whole number

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3
Q

what is a rational number

A

includes numbers that can be expressed as a fraction or ratio

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4
Q

what is irrational number

A

a number which cannot be expressed exactly as a fraction

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5
Q

what is a real number

A

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

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6
Q

what is an ordinal number

A

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

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7
Q

benefits of using hexadeciamal ?

A
  • 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
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8
Q

what is two’s complement and the method?

A

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
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9
Q

what is fixed point binary

A

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

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10
Q

The common prefixes used to represent bytes

A
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11
Q

Uncommon, more accurate prefixes to represent bytes

A
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12
Q

What is ASCII

A

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

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13
Q

what is Unicode

A

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

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14
Q

what is a transmission error

A

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

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15
Q

what are the four methods of error detection

A
  • parity bits
  • majority voting
    • check digits
      • checksums
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16
Q

How is a parity bit used for error detection

A
  • 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
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17
Q

how is majority voting used for error detection

A
  • 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
18
Q

how are checkdigits used for error detection

A
  • 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
19
Q

How is a checksum used for error detection

A
  • 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
20
Q

what are bitmapped graphics, common forms?

A

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

  • JPG
  • GIF
    • PNG
21
Q

what is colour depth

A
  • 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
22
Q

what is the image file size determined by?

A

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

23
Q

what is metadata

A

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
24
Q

what is metadata

A

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
25
Q

define analogue data

A

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

26
Q

define digital data

A

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

27
Q

What is sampling

A

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

28
Q

the process of analogue to digital conversion

A
  • 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
29
Q

what is sample resolution

A

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

30
Q

How do you calculate the file size of a sound file

A

file size = sample rate x resolution x length

30
Q

How do you calculate the file size of a sound file

A

file size = sample rate x resolution x length

31
Q

what is Nyquist’s theorem

A

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

32
Q

define compression

A

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

33
Q

define lossy data compression

A

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

34
Q

define lossless data compression

A

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

35
Q

what is run length encoding

A

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

36
Q

what is dictionary compression

A

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

37
Q

define encryption

A

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

38
Q

describe the process of encryption

A
  • 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
39
Q

describe the vernam cipher

A

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

Computer Science (8 decks)

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