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AQA AS Computer Science > Unit 5 - Fundamentals of data representation > Flashcards

Unit 5 - Fundamentals of data representation Flashcards

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1
Q

What are natural numbers?

A

All positive numbers

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2
Q

What are integer numbers?

A

All positive / negative numbers

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3
Q

What are rational numbers?

A

All fractional numbers

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4
Q

What are irrational numbers?

A

Numbers that can’t be written as a fraction

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5
Q

What are real numbers?

A

All positive or negative value and can include a fractional part

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6
Q

What are ordinal numbers?

A

Describe the position/placing of an item

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7
Q

What is a parity bit?

A

a bit set at the transmitting end for error detection

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8
Q

What is a check digit?

A

Additional digit at the end of a string to check for mistakes in input

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9
Q

What is majority voting?

A

Majority rule that assumes that if majority bits have not changed it is correct

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10
Q

What are analogue and digital signals?

A

Analogue - continouus

Digital - discrete

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11
Q

How is analogue converted into digital?

A
  • Sample measured by wave height
  • Translated into an integer value
  • Then converted and stored digitally as binary value
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12
Q

What is sampling?

A

Process of converting analogue to digital

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13
Q

What is sample resolution?

A

The number of bits used to record each measurement

- More bits = higher resolution (better accuracy)

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14
Q

What is sampling rate?

A

The frequency or number of samples per second

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15
Q

How do you calculate the file size?

A

File size (Bytes) = sample rate(Hz) x resolution(pixels)x length in seconds

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16
Q

What is Nyquist Theorem?

A

You must use a sampling rate at double the frequency of the original sound
fs > 2fmax

17
Q

What is MIDI?

A

Musical Instrument Digital Interface

  • Allows electronic musical instruments to communicate with each other
  • Uses less disk space than digital recording
18
Q

What are event messages?

A

Sends and receives specific messages to each device

  • Duration of note
  • Pitch
  • Volume change
  • Vibrato
  • Tempo
19
Q

What is bitmap resolution?

A

The number of pixels used to make up a bitmap image

- width x height

20
Q

What is colour depth?

A

The number of bits or bytes allocated to represent the colour of a pixel in a bitmap
- storage = resolution x colour depth

21
Q

What is metadata?

A

data about data

  • date created
  • colour depth etc
22
Q

What does reducing data size do?

A
  • Data sent more quickly
  • Less storage required
  • Less bandwith used
23
Q

What is lossy compression?

A

Non-essential data is
permanently removed
- JPEG & MP3
- Loses original data

24
Q

What is lossless compression?

A

No data removed but data is rearranged to be more efficient

  • Higher file size
  • No loss in quality
25
Q

What is run length encoding?

A

Groups together repeated bits

26
Q

What is dictionary compression?

A

Spots regularly occurring data and stores it
separately in a dictionary
- Produces additional data for the dictionary itself

27
Q

What is encryption?

A

data that cant be understood and needs to be decrypted to be understood

28
Q

What is Caesar cipher?

A

An old encryption but Julius Caesar

- realigining alphabet and shifting to encrypt

29
Q

Disadvantages of Caeser cipher

A
  • Only 25 possible keys
  • Only encrypts letters
  • Key is constant, so when one match is found, rest will be easily found
30
Q

What is the Verman cipher (One time pad cipher)?

A

A key that is only used once to encrypt and decrypt a message and is then discarded

  • Truly random
  • more or equal length of plain text
  • Used XOR logic gates
31
Q

Why is the Verman cipher ‘perfect security’?

A
  • Truly random
  • Never reused
  • Must be kept secret
32
Q

Limitations of Verman cipher

A
  • Key must be more or equal size
  • They must be random every time
  • Long keys hard to remember
33
Q

What is two’s compliment

A

A method of working with signed binary values.

34
Q

What is fixed point binary?

A

A way of representing binary fractions

AQA AS Computer Science (9 decks)

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