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Dan’s GCSE Computer Science > Topic 3 - Fundamentals Of Data Representation > Flashcards

Topic 3 - Fundamentals Of Data Representation Flashcards

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1
Q

what is the capacity of a device ?

A

how much data the device can store

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2
Q

What is a bit ?

A

The smallest unit of data that we can store is called a binary digit, or a bit for short.

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3
Q

what is the value of bit ?

A

The value of a bit can be either a 0 or a 1

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4
Q

Why do we not normally use bits to measure data ?

A

Because a bit is so small

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5
Q

what are the smaller ways to measure data ?

A

Nibble (4 bits).

Byte (8 bits).

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6
Q

what are common (large) units of storing data ?

A 
Kilobyte (KB) (1000 bytes).
Megabyte (MB) (1000 KB).
Gigabyte (GB) (1000 MB).
Terabyte (TB) (1000 GB).
Each unit is 1000 times the size of the previous unit
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7
Q

To calculate the amount of data that can be stored within a certain capacity, what three things do you need ?

A

size of the data being stored
how to convert between units
available capacity

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8
Q

The bigger the size of the data being stored, what does this mean for the capacity media ?

A

The bigger capacity media will be needed.

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9
Q

if a device has more capacity, what does this mean for the data ?

A

The more capacity available, the more data we can store.

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10
Q

An online video streaming service sends data at 4 MB per second. I only have 180 MB of data left. How long will I be able to watch the stream for?

A

45 seconds

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11
Q

I want to make a backup of 125 photos, which each take up 16 MB of disk space. What is the minimum amount of secondary storage space that I need, in GB?

A

Required capacity = number of files × size of a single file

Required capacity = 125 × 16 MB = 2,000 MB

convert from 2000MB to GB

2000MB/1000 = 2 GB

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12
Q

I need to download two videos, of average size 500 MB. What is the total amount of data that I will download?

A

1 GB

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13
Q

How many Kilobytes are there in four Gigabytes?

A

1,000 MB
1,000 × 4 = 4,000 MB
1,000 × 4,000 = 4,000,000 KB

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14
Q

In everyday life what number system do we use ?

A

denary
We use 10 symbols to represent each digit.
Each digit’s place value is multiplied by 10 as we move from right to left

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15
Q

what number system do computers use ?

A

Binary
Binary is an identical system, except using two symbols for each digit.
Only 1 and 0 are used in binary.
Each digit’s place value is multiplied by two as we move from right to left.

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16
Q

what is hexadecimal ?

A

Hexadecimal uses 16 different symbols for each place.
Hexadecimal uses the digits 0-9 then A-F:
A = 10 in denary, B = 11 …
Each digit’s place value is multiplied by 16 as we move from right to left.

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17
Q

Convert 10101 from binary to denary

A

21

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18
Q

How do you convert from Binary to hexadecimal ?

A

group into groups of 4 bits:
.
Start grouping from the right-hand side
Convert each 4 bit group separately.

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19
Q

How do you convert from Hexadecimal to binary ?

A

splitting each digit into 4 bits:

Separately convert each hexadecimal digit into 4 bits of binary.

Put all of the 4 bit groups together.

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20
Q

True or false: Some numbers can be represented in binary but not hexadecimal.

A

False

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21
Q

What is the easiest way to convert from denary to hexadecimal ?

A

The easiest method to convert denary numbers to hexadecimal is to first convert the denary to binary, and then use the binary to hexadecimal conversion algorithm.

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22
Q

How do you convert from hexadecimal to denary ?

A

Write out the powers of 16 above each hexadecimal digit.

For each place column, multiply the hexadecimal digit by the power of 16 above it.

Add together all of these results.

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23
Q

Convert 24 from hexadecimal to denary

A

Convert 24 from hexadecimal to denary:

Write out the powers of 16 above the digits
 16   1
 2   4

Multiply the digits by the power above them
16 × 2 = 32
1 × 4 = 4

Add the values together
32 + 4 = 36

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24
Q

Convert 15 from denary to binary

A

1111

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25
Q

Convert 0011001 from binary to hexadecimal

A

Split into groups of four bits
001     1001

Convert each digit separately
1       9

Put digits together
19

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26
Q

When grouping digits, you should group digits in which direction?

A

right-to-left

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27
Q

Why is hexadecimal good to use rather then binary ?

A

Hexadecimal is faster for humans to process than binary.

Hexadecimal allows us to find errors more easily.

Hexadecimal is used in every computer system

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28
Q

what are the advantages of hexadecimal ?

A

An 8-bit binary number can be represented by two hexadecimal digits.

This means you can reduce storage space and processing time with hexadecimal than with binary.

Hex is easier and faster to write two digits than the full binary sequence.

It is easier for a human to process hexadecimal than binary.

Using hexadecimal

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29
Q

what programming languages use hexadecimal ?

A

Hexadecimal is used extensively in programming languages such as:
Machine code.
Assembly.

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30
Q

when in programs is hex used when writing programs ?

A

Hex can be used during the debugging stage of writing programs as it is easy to process by humans.

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31
Q

what can hex represent ?

A

Hex can represent numbers stored in a CPU’s registers or in main memory.

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32
Q

What’s a MAC address

A

a number that uniquely identifies a networked device

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33
Q

In binary addition, if we add 0 + 0 what do we get ?

A

0

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34
Q

In binary addition, if we add 1 + 0 (or 0 + 1) what do we get ?

A

1

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35
Q

In binary addition, if we add 1 + 1 what do we get ?

A

we cannot use the symbol 2. So we need to carry the 1 and put 0 in the current place.

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36
Q

In binary addition, if we have 1 + 1 and also a 1 carried over from the previous column what do we get ?

A

carry the 1 and have 1 left over.

So we carry 1 and put 1 in the current place.

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37
Q

What is an overflow error ?

A

If a number is carried past the last place column

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38
Q

Are Binary numbers stored as a fixed length ?

A

Yes

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39
Q

What can overflow errors cause ?

A

inaccurate results and software crashes

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40
Q

What is a technique for performing multiplication or division on a binary number ?

A

A binary shift

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41
Q

What happens in a right binary shift ?

A

each digit is moved one place to the right.

This has the effect of dividing the number by two

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42
Q

Why must you take care when performing a right shift ?

A

So that no data is shifted off the right hand side as this can cause a loss of accuracy.

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43
Q

What happens in a left binary shift ?

A

each digit is moved one place to the left.

This has the effect of multiplying the number by two.

44
Q

Why must you take care, when performing a left shift

A

So that there is no overflow error (where we run out of space to store the last digit of the number).

45
Q

What are added to the start or end of the binary number to fill any missing spaces after a binary shift has been performed ?

A

Extra 0 bits

46
Q

01100110

01010101+

A

10111011

47
Q

What is text data made up of ?

A

characters

48
Q

What do character sets allow us to store ?

A

characters digitally

49
Q

What is a Character set ?

A

A character set is a collection of all the characters that a computer recognises, along with their binary codes

50
Q

What is each character assigned?

A

It’s own character code.

51
Q

What are the two main character sets ?

A

American Standard Code for Information Interchange

Unicode

52
Q

What are in character sets ?

A

Alphanumeric characters e.g. letters, numbers, and symbols.

Special characters e.g. new line.

53
Q

What character set is the most common ?

A

The American Standard Code for Information Interchange (ASCII)

54
Q

Each character in ASCII is represented by what ?

A

a seven-bit binary code.

55
Q

What is the maximum amount of characters in ASCII ?

A

That means there is a maximum of 128 characters

56
Q

What is in ASCII ?

A

ASCII includes all commonly used letters and symbols in the English language.

57
Q

In ASCII each letter is represented by how many bits ?

A

seven bits.

58
Q

Why is ASCII using seven bits useful ?

A

because when used in an 8-bit system, the extra bit can be used as a check digit.

59
Q

What are the limitations of ASCII ?

A

128 characters is perfectly fine for the English language. But it does not leave space for characters from other languages.

An extended ASCII set was released which used all eight bits, but it was still not enough.

This led to the release of Unicode.

60
Q

What is included in ASCII?

A

All commonly used letters and symbols in English

61
Q

Why was the character set Unicode released ?

A

because of the need to standardise character sets internationally.

62
Q

What does Unicode aim to represent?

A

every possible character in the world.

The most common form of Unicode is UTF-8, and uses between eight and 48 bit binary codes to represent each character.

63
Q

How is Unicode compatible with ASCII ?

A

The first 256 characters in Unicode are identical to extended ASCII, which makes it backwards compatible with documents encoded using older character sets.

64
Q

What are the types of characters in Unicode ?

A

Unicode represents characters from all major alphabets of the world.

Unicode is also used to represent emojis!

65
Q

Why are the first 256 characters in Unicode identical to extended ASCII?

A

For backwards compatibility

66
Q

What is the main drawback of ASCII?

A

The lack of international language support

67
Q

How are most digital images stored ?

A

as bitmaps

68
Q

A bitmap image is split up into tiny squares called what ?

A

pixels

69
Q

In a bitmap image how are the colours of each pixel stored ?

A

as a binary number

70
Q

The amount of bits used to store the colour of each pixel is known as what ?

A

the colour depth

71
Q

If there is a greater number of bits used to represent each pixel, what does this mean for the colours ?

A

The more unique colours can be stored.

72
Q

What are the common colour depths ?

A

1-bit, 8-bit, 16-bit, and 24-bit.

73
Q

What’s resolution ?

A

the number of pixels in an image.

74
Q

How do you find the number of pixels ?

A

multiplying the width by the height of the image.

75
Q

What’s an example of resolution ?

A

An example resolution is 1080p which is 1920x1080

76
Q

What is metadata ?

A

Metadata is extra information that is added to an image file

77
Q

What are examples of metadata ?

A

The resolution.
The colour-depth.
The encoding format.
The time and date of taking the photo

78
Q

How do you find file size of an image (in bits) ?

A

File size (in bits) = image width x image height x colour depth (in bits)

79
Q

How do you work out file size of an image (in bytes) ?

A

File size (in bits) = image width x image height x colour depth (in bits)

File size (in bytes) = file size (in bits) ÷ 8

80
Q

What are all images stored as ?

A

binary

81
Q

In a black and white image, how is each pixel represented ?

A

By 1 bit
A 0 will represent a black area.
A 1 will represent a white area

82
Q

How do you convert binary to image ?

A

In a black and white image, each pixel is represented by 1 bit:
A 0 will represent a black area.
A 1 will represent a white area.

The image will be represented by a binary string. Use the value of each bit to colour each pixel in the right colour.

The binary string starts at the top-left of the image, and represents the first row, followed by the second row, and continues until the end of the image.

83
Q

How do you convert from image to binary ?

A

Each pixel of the image will be represented by one bit of the binary string.
Starting at the top left, and working across the first row:
Write a 0 if the pixel is black.
Write a 1 if the pixel is white.
Continue this process until the end of the image.

84
Q

An image has a 500 pixel width, a 250 pixel height and a colour depth of 8-bit.

What is the size of the image file in bytes?

A

500 x 250 x 8 = 1000000

1000000/8 = 125000

85
Q

How do you work out the resolution of an image ?

A

The resolution of an image is the number of pixels in the image. It is specified as the
width × height of the image.

86
Q

How does sound travel ?

A

Sounds travels as analogue waves

87
Q

What do computers need to convert analogue waves into ?

A

computers need to convert this to a digital format

88
Q

What is sampling ?

A

When sound is recorded by a computer its amplitude is recorded at regular intervals.

The value of the amplitude at each sample is stored as a binary value.

89
Q

What is sampling rate ?

A

The number of samples taken per second

90
Q

What is sample size ?

A

The number of bits used to store each sample

91
Q

When you increase the sampling rate what happens to the quality of the audio ?

A

The quality of the audio will increase

92
Q

When you increase the sample size what happens to the quality of the audio ?

A

The quality of the audio will increase

93
Q

What is the problem with increasing the sampling rate and sampling size ?

A

Unfortunately, increasing these make the file size larger.

94
Q

What is bitrate ?

A

The bit rate is the amount of data stored per second of audio.

95
Q

How do you calculate bitrate ?

A

bitrate = sample rate x sample size

96
Q

What is the bitrate of an audio track with a sample rate of 1,000 Hz and a sample size of four bits?

A

Bit rate = sample size × sample rate

Bit rate = 4 × 1,000 = 4,000 bps (bits per second).

97
Q

Representing audio, images, and especially video take up a lot of secondary storage space.

What helps to reduce the size of these files so that we can store more data ?

A

Compression

98
Q

What are the two types of compression ?

A

Lossy compression

Lossless compression

99
Q

What is lossy compression ?

A

An algorithm is applied to remove unnecessary detail from the original file.

Some data is permanently lost, but enough remains so that the file is still useful and there is barely a noticeable difference.

Lossy compression results in dramatic file size reduction.

100
Q

What is lossless compression ?

A

None of the original data is lost.

An algorithm can be used to perfectly restore the original file when needed.

This is especially useful for executable files, where all of the data is necessary.

Lossless compression causes file size to reduce moderately.

101
Q

What’s an example of a compression algorithm ?

A

Run length encoding (RLE)-lossless

Huffman coding-lossless

102
Q

What is run length encoding ?

A

Run length encoding (RLE) is a form of lossless compression that replaces repeating sequences of 0s and 1s with more efficient representations.

Each repeating string will be replaced by a code which represents the character and the amount of times it is to be repeated.

103
Q

What’s Huffman coding ?

A

Huffman coding is a text compression algorithm which provides lossless compression.

Huffman coding can reduce file sizes considerably by assigning a fewer number of bits to the most frequently used characters.

104
Q

When is Huffman coming normally used ?

A

for long pieces of text data.

105
Q

What is lossy compression appropriate for ?

A

Videos
Images
Audio

106
Q

Why is run length encoding difficult in images?

A

Adjacent pixels have similar colours

Dan’s GCSE Computer Science (8 decks)

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