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Computer Science GCSE > Chapter 4: Data Representation > Flashcards

Chapter 4: Data Representation Flashcards

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1
Q

Bit

A

A single binary digit: 1 or 0

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2
Q

Nibble

A

4 bits

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3
Q

Byte

A

8 bits

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4
Q

Kilobyte

A

1024 bytes (2¹⁰ bytes)

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5
Q

Megabyte

A

1024 kilobytes (2²⁰ bytes)

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6
Q

Gigabyte

A

1024 megabytes (2³⁰ bytes)

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7
Q

Terabyte

A

1024 gigabytes (2⁴⁰ bytes)

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8
Q

What is the order of the various kinds of bytes? (Up to terabytes needed)

A
  1. Byte
  2. Kilobyte
  3. Megabyte
  4. Gigabyte
  5. Terabyte
  6. Petabyte
  7. Exabyte
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9
Q

Binary

A

The base 2 number system, which consists of the digits 1 and 0. Used by computers

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10
Q

Why is binary used in computers?

A

Computers consist of millions of transistors, which are switches that are either on (to store a 1) or off (to store a 0)

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11
Q

Denary

A

Base 10, which uses the digits 0 through 9. The system we use in everyday life

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12
Q

Hexadecimal

A

The base 16 number system, which uses the digits 0-9 and the letters A-F. Used to represent groups of four bits at a time

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13
Q

Why is hexadecimal number representation often used?

A

Hexadecimal is generally easier for people to remember than binary

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14
Q

How would you write the denary number 84 in binary?

A

1010100

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15
Q

How would you write the denary number 182 in hexadecimal?

A

B6

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16
Q

How would you write the hexadecimal number FF in denary?

A

255

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17
Q

How would you write the binary number 11111111 in denary?

A

255

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18
Q

How would you write the binary number 01011100 in hexadecimal?

A

5C

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19
Q

How would you write the hexadecimal number 4E in binary?

A

01001110

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20
Q

How would you store a real number in binary?

A

Store the main part of the number (the mantissa) and the number of times it needs to be multiplied by 10 (the exponent)

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21
Q

How would you store a date in binary?

A

Each date would be stored as a unique number within a certain range of dates and time

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22
Q

Character set

A

The set of symbols that can be represented by a computer, which includes letters, digits, punctuation and control characters

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23
Q

How is each character in a character set represented?

A

Each character is represented by a numerical code stored as a binary integer

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24
Q

What are some examples of character sets? (3)

A
  1. ASCII
  2. Unicode
  3. EBCDIC
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25
Q

ASCII

A

American Standard Code for Information Interchange: a 7-bit character set used by PCs. There is also an extended set that uses 8 bits

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26
Q

What is the ASCII code for the space key?

A

32

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27
Q

What is the ASCII code for ‘A’?

A

65

28
Q

What is the ASCII code for ‘a’?

A

97

29
Q

Explain the possible limitations of using the ASCII character set for global communication (4 marks)

A
  1. ASCII uses 7 bits to represent each character
  2. This means that it can only represent 128 (2⁷) different characters
  3. This is enough to represent the letters and punctuation used in English
  4. Some languages have much larger alphabets
  5. Global communication would require a character set that contains all of the alphabets in the world - much more than even the 256 in extended ASCII (8 bits)
30
Q

Analogue

A

A continuously changing wave e.g. natural sound

31
Q

Digital

A

Data made up of separate values. How data is stored on a computer

32
Q

How is a sound wave converted from analogue to digital? (2)

A
  1. The amplitude (height of the wave) is measured at regular intervals (sampling)
  2. These values are stored as a series of binary numbers in a file
33
Q

What do the amplitude and frequency of a sound wave control?

A

Amplitude: how loud the sound is
Frequency: the sound’s pitch

34
Q

What is sound quality affected by? (2)

A

Sample resolution: the more bits used, the better the accuracy of the sound file
Sample interval: the smaller the interval, the better the quality of playback

35
Q

Sample rate

A

The number of samples taken per second

36
Q

Sample interval

A

The time gap between measurements of the sound wave being taken. A different way of expressing the sample rate

37
Q

What is the sample rate of:

  1. A CD?
  2. A telephone network?
A
  1. 41.1 kHz

2. About 8 kHz

38
Q

Sample resolution OR Bit depth

A

The number of bits used to store each sample

39
Q

What is the sample resolution of a CD?

A

16 bit, which produces a good sound quality

40
Q

Sound synthesis

A

When sound stored in a file is recreated by the computer using a DAC and played through speakers

41
Q

What bit depth and sample rate is becoming more common?

What is the advantage and disadvantage of this?

A

Bit depth: 24 bit
Sample rate: 96 kHz

Pro: sound quality is better
Con: file sizes are huge

42
Q

What are two commonly used uncompressed audio file types?

A
  1. WAV

2. AIFF

43
Q

Pros and Cons of WAV and AIFF formats (1 | 2)

A

Pros
1. High sound quality

Cons

  1. Large file sizes
  2. Do not work well for streaming or downloads
44
Q

Compression

A

A technique which reduces a file’s size by changing its format

45
Q

What are the two types of compression?

A
  1. Lossy: permanently removes data

2. Lossless: no loss of quality, and can be restored to pre-compression state

46
Q

MP3

A

A commonly used, lossy audio compression format

47
Q

How do MP3s work?

A

They work by removing frequencies outside the range of human hearing. MP3s can reduce the file size to a twelfth of the original depending on the chosen bitrate

48
Q

Pros and Cons of MP3s (2 | 1)

A

Pros

  1. Ideal for streaming and downloading
  2. Can be used easily on portable devices e.g. mobile phones

Cons
1. Musicians claim that even the highest bitrate MP3s do not produce the sound quality of a WAV or AIFF

49
Q

Bitmap image

A

An image that is stored as a series of values per pixel. Also known as a pixelmap or raster graphics

50
Q

What are three common image file types?

A
  1. JPEG
  2. GIF
  3. PNG
51
Q

Pixel

A

Short for “picture element”, the smallest component of a bitmap image

52
Q

Colour depth

A

The number of bits used to represent the colour of a single pixel in a bitmap image

53
Q

Higher colour depth provides…

A

A broader range of distinct colours

54
Q

What is the colour depth of an image with 4 colours?

A

2 bits per pixel

55
Q

What is the colour depth of an image stored as a GIF?

A

8 bits, allowing a total of 256 different colours

56
Q

Resolution

A

The number of pixels in an image expressed as: number of pixels across * number of pixels down

57
Q

Metadata

A

Data that serves to provide context or additional information about other data e.g. a file

58
Q

What is the metadata in the case of image files?

A

The data the computer needs to interpret the image data in the file e.g. image format, resolution, colour depth and image dimensions

59
Q

How does a JPEG compress a bitmap file?

A

It is a lossy compression format that works by discarding details that are generally undetectable by the human eye

60
Q

What is another way of storing images besides bitmap files?

A

Vector graphics, which consist of lines with properties such as style, colour, start point and end point. Each of these properties are stored as binary in a file

61
Q

Data

A

Facts and figures with no context or format to give them meaning

62
Q

Information

A

Data that has been given meaning

63
Q

ADC

A

Analogue to Digital Converter: takes real-world analogue information and converts it into a binary representation, which can be stored on a computer

64
Q

DAC

A

Digital to Analogue Converter: converts digital data into an analogue signal

65
Q

In terms of information and data, what do (1) input devices and (2) output devices do?

A
  1. Input devices take real-world information and store it as data
  2. Output devices take data from the computer and present it as information to the user

Computer Science GCSE (8 decks)

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