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Computing > U3 - Data representation > Flashcards

U3 - Data representation Flashcards

1
Q

What is the MSB

A

The most significant bit is the bit with the largest value (the bit that is furthest to the left)

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2
Q

What is the LSB

A

The least significant bit is the bit with the smallest value (the bit that is furthest to the right)

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3
Q

What is the largest number you can represent in 1 byte?

A

255 (but 256 numbers can be represented)

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4
Q

Advantages of hex (4)

A
  • It is much simpler to remember a hex value than a binary value
  • It is quicker to write or type since a hex digit only takes up one digit rather than 4 bits
  • People are less likely to make an error with fewer digits
  • It is easy to convert between hex and binary
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5
Q

Define overflow error

A

An overflow error occurs when the result of a binary addition is too large for the number of bits the computer works with

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6
Q

What effect does a binary shift left have on a number?

A

It doubles the number

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7
Q

What effect does a binary shift right twice have on a number?

A

It halves the number and rounds down each time

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8
Q

Define a character set

A

A set of letters, symbols and digits that can be represented by a computer

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9
Q

2 major character sets in use today

A

ASCII and unicode

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10
Q

How does ASCII encode characters?

A

It encodes 128 characters into 7-bit binary code

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11
Q

What is extended ASCII and how many characters can it encode?

A

Extended ASCII is an 8-bit character code to allow for many more characters to be represented e.g. copyright symbol. 256 different characters can be encoded

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12
Q

How does unicode encode characters?

A

It encodes 65,536 characters into 16-bit codes

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13
Q

What are bitmap images made up of?

A

Pixels

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14
Q

Define pixel

A

The smallest identifiable area of an image

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15
Q

How can a pixel’s colour change?

A

By changing the binary value of the colour

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16
Q

Define resolution

A

The concentration of pixels within a specific area

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17
Q

What happens when you have more bits per pixel?

A

More colour combinations

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18
Q

Bit depth in comparison to colour combinations examples

A

1 bit = 2 colours
2 bits = 4 colours
3 bits = 8 colours
4 bits = 16 colours

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19
Q

Higher bit depth

A

Gives a greater range of colour and a better quality of image

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20
Q

How does the number of colours affect file size?

A

An increase in the number of colours that are used in an image (the bit depth) will increase the file size

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21
Q

How does the size of the image affect file size? (2 meanings)

A
  • An increase in the number of pixels in the image, will increase the file size
  • If an images physical size is increased by making each pixel larger then there is no change in the file size
22
Q

What does 0 and 1 correspond to?

A 
0 = black
1 = white
23
Q

What three colours does each pixel have a proportion of?

A

Red, green, blue

24
Q

Why are colour values expressed as decimal RGB values and hex rather than binary?

A

RGB values and hex are easier for people to read, write and remember and reduce errors if copied

25
Q

Formula for bitmap image file size (MB) in bits and in bytes

A

BITS:
Width x height x colour depth

BYTES:
(Width x height x colour depth) / 8

26
Q

Define metadata

A

Holds data about the image, such as colour depth, resolution, date created, author

27
Q

What data type are analogue sound signals?

A

Continuous

28
Q

What data type are digitial sound signals?

A

Discrete. This means the sound wave is sampled at regular intervals

29
Q

How is sound digitised?

A

By repeatedly measuring and recording the sound wave

30
Q

Why do sounds have to be converted into a digital form?

A

In order to be stored and processed by a computer

31
Q

Define sound sample

A

A measurement of amplitude of a sound wave at a given time

32
Q

How is sound sampled

A

Using a sample resolution (bit depth) and sampling rate

33
Q

What does the sampling resolution determine?

A

How closely the wave is sampled on the y-axis

34
Q

What is the sampling rate? What is it measured in?

A

The number of samples taken per second, measured in hertz (Hz)

35
Q

Define sample resolution / bit depth

A

The number of bits used to record each measurement

36
Q

What does more bits used per sample enable?

A

More bits used per sample enables the height of the wave to be more accurately measured, but this increases file size

37
Q

1 Hz =

A

1 sample per second

38
Q

Formula for calculating sound file sizes

A

File size (bits) = sampling rate x resolution x duration

39
Q

What does recording quality mean (2)

A
  • We sample the sound more frequently

- We record the wave height more accurately

40
Q

Define lossy compression

A

Compression that removes sounds that we can’t easily hear or that least affect the perceived playback quality.

41
Q

What is lossy compression useful for?

A

Storing, downloading or streaming

42
Q

Define lossless compression

A

Compression that is able to reduce the file size when compressed without losing any data

43
Q

Examples of lossless music file formats

A
  • FLAC
  • ALAC
  • WMA Lossless
44
Q

Examples of lossy file formats

A
  • MP3

- AAC

45
Q

Define compression

A

Algorithms which reduce the amount of bits required to represent data. This reduces the file size.

46
Q

Define decompression

A

The process where compressed data is restored to its original format

47
Q

What is the difference between lossy and lossless compression?

A

Lossy compression permanently loses some data, whereas lossless compression will not lose any of the original data

48
Q

What is RLE

A

An algorithm that uses frequency/data pairs to encode each run length of the same coloured pixel

49
Q

Advantages of using compression (3)

A
  • Download times are reduced
  • Data allowances go further
  • Smaller files = fewer packets = faster transmittion time. This reduces traffic over the internet
  • Streaming is possible as the data can be sent as fast as the rate it is played at
  • Images inside web pages appear faster
  • Reduces space on disk / servers
50
Q

When does buffering occur?

A

When the download speed is slower than the playback speed

51
Q

Lossless file formats

A

PICTURES:
PNG, GIF

DOCUMENT:
ZIP

MUSIC:
FLAC/ALAC

52
Q

Lossy file formats

A

PICTURES:
JPEG

VIDEO:
MP4

MUSIC:
MP3

Computing (8 decks)

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