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Computer Science > Unit 2 - Data representation > Flashcards

Unit 2 - Data representation Flashcards

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1
Q

Why is hexadecimal used instead of binary?

Binary

Mark scheme answer

A
  • Easier/quicker to communicate / enter /write / read / remember
  • Less chance of input errors // easier to spot errors
  • They are shorter
  • Easy to convert between binary and Hexadecimal
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2
Q

How can transistors be used to store a value in binary?

Binary

Mark scheme answer

A
  • Transistor has two states
  • 1 represents on, 0 represents off
  • Each transistor stores one bit
  • Multiple transistors used to store a binary value
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3
Q

Why do computers represent data in binary form?

Binary

Mark scheme answer

A

Computers consist of transistors / switches which only have values 1 or 0

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4
Q

What does a left shift do?

Binary

A

Multiply binary by 2

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5
Q

What does a right shift do?

Binary

A

Divide binary by 2

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6
Q

What are the 2 character sets?

Characters

A
  • ASCII
  • Unicode
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7
Q

What is ASCII?

Characters

A

American Standard Code for Information Interchange has become the standard code used globally. It uses a 7-bit binary code to encode 128 letters.

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8
Q

Why was Unicode developed?

Characters

A

ASCII is not enough to represent different languages and emojis, many more characters are needed.
For that reason Unicode was developed, including 16-bit or even a 32-bit to give over 4 billion combinations.

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9
Q

How is a character set used to represent a string?

Characters

Mark scheme answer

A
  • Each character has a unique (binary) value
  • Each character in the string is assigned its associated number/value
  • The (binary) value of each character is stored
  • Uses ASCII/Extended ASCII/Unicode
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10
Q

What are image file types?

Images

A

BMP
JPG
GIF
PNG
TIFF
Vector: SVG

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11
Q

What is a pixel?

Images

A

Pixels is the smallest identifiable area of an image, each pixel is given a binary value to represent it.

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12
Q

What is a bitmap image?

Images

A

Bitmap images are made up of pixels.
Resolution is the concentration of pixels within a specific area. It’s area is defined by the height and width of the image in pixels (PPI or DPI)
Each value in a pixel represents a certain colour.

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13
Q

What is bit depth?

Images

A

The more bits there are in a pixel, the more colour combinations there are.
Each pixel can only represent a specific number of colours, the combination is the bit depth in terms of 2^n (n being the number of bits). Higher bit depth gives a greater range of colour and a better quality of image.

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14
Q

How can increasing colour depth affect image?

Images

Mark scheme answer

A
  • The quality of the image can be improved
  • The file size will increase
  • The number of colours that can be
    represented/used will increase
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15
Q

How do you calculate bits required for an mage?

Images

A

Bits for image = Number of pixels x colour depth

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16
Q

What is a monochrome image?

Images

A

Monochrome images only use colour black (0) and white (1). They only store the binary value, the image dimension. You can change the colour by changing the binary value.

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17
Q

How does color work in an image?

Images

A

Each pixel has a proportion of red,green and blue to make up its colour. Colour values of individual pixels are expressed in software as denary RGB values and in hexadecimal. These are better to use as it is easier for people to read, write and remember and can reduce the errors when copied.

18
Q

What is meant by the term image resolution?

Images

Mark scheme answer

A
  • Number of pixels (in image)
  • Height and width (of image)
19
Q

What is metadata?

Images

Mark Scheme answer

A

Data about data / the image/file //
properties of the file

20
Q

Examples of metadata of an image

Images

A

Height
Width
Colour/bit depth
Date
Geolocation
File size
File type
Compression type
Author

21
Q

How are bitmap images are represented in binary?

Images

Marks scheme answer

A

Image made of / split up into pixels
Each pixel given a binary code which represents the colour of that pixel
Each colour is given a different/unique
binary code. Metadata stored alongside the image

22
Q

How is an analogue sound wave is converted into digital form?

Sound

Mark scheme answer

A
  • sound wave is sampled amplitude/height (of wave) is measured regular time intervals
  • Each sample/measurement is stored as a binary number
  • The binary number for each sample is stored sequentially
23
Q

Why is analogue sound converted?

Sound

A

Sound must be converted into a digital form so the computer can process and store it. Sound wave has to be repeatedly measured and recorded to be digitised.

24
Q

What is a sound sample?

Sound

A

Sound sample is measurement of amplitude of a sound wave area given time. Sound is sampled using the sample rate and bit depth.

25
Q

What is bit depth in a sound wave?

Sound

A

determines how closely the wave is sampled on the y-axis

26
Q

What is sample rate/frequency?

Sound

Mark scheme answer

A

Sample rate is the number is samples taken per second (measure in Hz)

27
Q

What is sample resolution?

Sound

A

Sample resolution is the number of bits (audio bit depth) used to record each measurement.

28
Q

How do you work out sound file size?

Sound

A

File size (bits) = sample rate x bit depth x duration

29
Q

How can sound quality be improved?

Sound

A
  • Sampling the sound more frequently
  • Sampling the sound more accurately to record the wave height
  • Increasing the bit rate to improve the accuracy of data points
    Increasing any of these also increases the file size of the audio
30
Q

How can the file size of the sound recording be reduced?

Sound

Mark scheme answer

A
  • Reduce the sample rate so fewer samples are taken per second
  • Reduce the bit depth so less data is used for each sample
  • Use lossy compression to remove data
  • Use lossless compression to identify patterns in the data/store this more efficiently
  • Reduce the length of the sound file
31
Q

What data is recorded when sound is sampled?

Sound

Mark scheme answer

A

The height of the wave as a numerical value

32
Q

How does lossy compression work in a sound file?

Sound

A

Lossy compression removes sound that cannot be heard very easily or does not affect the playback quality

33
Q

What are features of lossy compression in a sound file?

Sound

A
  • Can possibly affect the wound quality
  • Can decrease the file size by a large amount
  • Useful for storing, downloading and streaming
34
Q

How does lossless compression work in a sound file?

Sound

A

Lossless compression allows the file size to be reduced but does not require any information to be deleted.

35
Q

What is compression?

Compression

A

Compression is the name given to algorithms which reduce file sizes. Compression is heavily used with sound, image and video files

36
Q

What are the 2 types of compression

Compression

A
  • Lossy
  • Lossless
37
Q

How do you reduce file size of an image?

Compression

Mark scheme answer

A
  • Reduce number of pixels / resolution
  • Reduce number of colours
  • Use lossy compression
  • Use lossless compression
38
Q

What are advantages of lossy compression in an image?

Compression

Mark scheme answer

A
  • File size is reduced so quicker to upload / download
  • takes up less storage space
  • permanent reduction
39
Q

What are disadvantages of lossy compression in an image?

Compression

Mark scheme answer

A
  • Quality of image is reduced
  • because data is lost / removed
  • reduction is permanent / not
    reversible
40
Q

What are benefits of compressing data?

Compression

A
  • Reduces file size
  • Takes less time to transmit // faster to upload / download
  • Requires less storage space
  • May otherwise exceed email storage
  • Uses less bandwidth to transmit
  • Uses less data to send
41
Q

Which compression is most suitable for text?

Compression

Mark scheme answer

A

Lossless will not remove any data text files will not work if any data is lost

42
Q

Which compression is most suitable for image?

Compression

Mark scheme answer

A

Lossy will reduce the file size more significantly
Image will only lose quality and make unnoticable changes

Computer Science (7 decks)

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