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Computer Science > Computer Systems (II) - Data Representation > Flashcards

Computer Systems (II) - Data Representation Flashcards

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1
Q

How do computers represent the flow of electricity?

A

1s and 0s

1 – electricity flowing

0 – electricity not flowing

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2
Q

What is a 0 or 1 in a binary code?

A

Each 0 or 1 in a binary code is a bit (binary digit)

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3
Q

How many bits is the binary code 1010?

A

4 bits

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4
Q

What is a byte big enough to store?

A

A byte can store one character (e.g. A, 1, £ etc…)

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5
Q

What two values can a bit take?

A

A 1 or a 0

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6
Q

Draw a table to represent the size of units of data

A
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7
Q

How many bits is a nibble?

A

4 bits

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8
Q

How many different values can a nibble take?

A

2 to the power 4 = 16x different values

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9
Q

How many different values can a byte take?

A

2 to the power 8 = 256x different values

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10
Q

How many bits are in a byte?

A

8 bits are in a byte

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11
Q

How many kB are in a B, MB in a kB, GB in a MB, TB in a GB and PB in a TB?

A

1000

*Units are sometimes defined as 1024 not 1000 as 1024 is a power of 2 which is helpful when dealing with binary

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12
Q

What base in binary?

A

Base 2 (binary)

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13
Q

What is our standard number system?

A

Denary (or decimal / base 10)

E.g. 0,1,2,3,4,5,6,7,8,9

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14
Q

In denary, what increase exists for the place value from right to left?

A

Powers of 10 (1000, 100, 10, 1)

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15
Q

In binary, what increase exists for the place value from right to left?

A

Powers of 2 (8, 4, 2, 1)

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16
Q

What are the binary equivalents of the denary 0-15?

A

0 = 0

1 = 1

2 = 10

3 = 11

4 = 100

5 = 101

6 = 110

7 = 111

8 = 1000

9 = 1001

10 = 1010

11 = 1011

12 = 1100

13 = 1101

14 = 1110

15 = 1111

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17
Q

What are most binary numbers given as?

A

8-bit numbers, e.g. 00110101

This can represent the denary numbers 0-256

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18
Q

The bit with the largest value of on what side?

A

The left-most bit

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19
Q

What is the left-most bit referred to as?

A

The most significant bit

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20
Q

What is the right-most bit referred to as?

A

The least significant bit

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21
Q

What does any non-zero number raised to the power 0 equal?

A

1

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22
Q

Draw out a table with binary place values to make a binary / denary conversion for the binary 00110101 and calculate the denary for this

A

00110101 = 53 in denary (add numbers with 1 in the column)

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23
Q

How can denary be converted to binary?

A

By subtracting (from largest to smallest)

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24
Q

Draw out a table to convert 79 into an 8-bit binary

A

79 = 01001111 in binary

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25
Q

How are binary numbers added together?

A

Column additions

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26
Q

What are the steps required for a binary addition?

A

Place the binary numbers into columns

Starting from the right, add numbers in the columns

When 1 + 1 = 10, carry the 1 into the next column

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27
Q

Add the binary numbers 10001101 and 01001000 together

A
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28
Q

In a binary addition if you come across 1 + 1+ 1 what should be done?

A

Write the 1, then carry 1 to the next column

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29
Q

Add the binary numbers 00110011 and 01111001 together

A
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30
Q

What causes an overflow error?

A

When a number has too many bits

E.g. 8-bit calculation 11111111 + 00000001 gives the 9-bit answer 100000000

The computer will see the 1 as an overflow error and return the result 00000000 – an overflow flag will be shown (storing the extra bits elsewhere)

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31
Q

What is a binary shift?

A

A binary / logical shift moves every bit in a binary number left or right (gaps are filled with a 0)

The direction of the shift indicates a multiplication or division

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32
Q

What is the difference between a left binary shift and a right binary shift?

A

A shift left multiplies and a shift right divides

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33
Q

Perform a 3-place binary shift to the left for the 8-bit binary number 00101001

A
34
Q

Perform a 2-place shift to the right for the 8-bit binary number 00101001

A
35
Q

What are hexadecimals?

A

Hexadecimals use base-16 and use a combination of digits and characters to represent the denary numbers 0-15

A hex character equals a nibble (going from 0-9 and then A-F)

36
Q

List the hex characters

A
37
Q

How is hex converted to denary?

A

Each character is multiplied

Moving right to left increases place values in powers of 16

38
Q

Convert the hexadecimal number 87 into denary

A

7 x 1 = 7
8 x 16 = 128
Hex 87 = 135 in denary

39
Q

How is denary converted into hex?

A

Each character is divided

Start at the left and divide, holding onto the remainders

40
Q

Convert the denary 106 into hexadecimal

A

106 / 16 = 6 (remainder 10)

10 / 1 = 10 (A)

41
Q

How do you convert binary to hex?

A

Split into nibbles – each hex character equals a nibble

42
Q

Convert the binary 10111001 to hexadecimal

A

8 + 2 + 1 = 11 (B)

8 + 1 = 9

43
Q

If a binary number cannot be split into nibbles, e.g. 111110 what must be done for a conversion into hexadecimal?

A

Zeros need to be added to the left to create nibble so the binary becomes 00111110
Hex = 3E

44
Q

How is hex to binary calculated? Give the example hex 8C to binary

A

Each character’s denary value is needed so 8 becomes 1000 and C becomes 1100

8C = binary 10001100

45
Q

How do computers process alphanumeric characters?

A

Characters are converted to binary code (and vice versa)

Character sets are used

46
Q

Name two character sets

A

ASCII and Unicode

47
Q

What do character sets include alongside letters, digits and symbols?

A

Special characters which perform commands

E.g. enter / delete

48
Q

Give two examples of special characters in a character set

A

Enter

Delete

49
Q

What are the features of ASCII?

A

Each character is given a 7-bit binary code (128x characters can be represented)

Includes all letters in English alphabet + numbers + symbols + commands

Extra bit added (0) at start to make 1 byte

50
Q

What does this table show?

A

ASCII table

51
Q

What are the features of Unicode?

A

Unicode tries to cover every possible letter or symbol in all languages

It uses multiple bytes for each character

The first 128 codes in Unicode are the same as ASCII

52
Q

What is the formula for working out the size of a text file?

A

File size (bits) = number of bits per character x number of characters

53
Q

What is the size of a text file using 8-bits per character (ASCII) containing 200x characters?

A

8 x 200 = 1600 bits

54
Q

How are images stored?

A

Images are stored as pixels

The colour is represented by binary

Greater range of colours / shades by increasing the number of bits

55
Q

What bit rate would the following image be represented by?

A

1-bit (black and white)

0 for white and 1 for black

56
Q

What bit rate would the following image be represented by?

A

2-bit (four colours)

00 for white, 01 for light grey, 10 for dark grey and 11 for black

57
Q

What do most modern devices use for their colour-depth?

A

24-bit colour which gives 16’777’216 colours

*Human eye estimated to see 10’000’000 colours

58
Q

Given the colour depth, what is the formula for working out how many colours can be made? Give exams for 1-bit, 4-bit and 24-bit

A

Total number of colours = 2 to the n

n = number of bits per pixel (bpp))

1-bit = 2 to the 1 = 2 colours
4-bit = 2 to the 4 = 16 colours
24-bit = 2 to the 24 = 16’777’216 colours
59
Q

What happens as colour depth / resolution increases?

A

File size increases

60
Q

What is image resolution?

A

The number of pixels in the image

Sometimes given as width x height

Higher resolution = better quality (but more data)

61
Q

How can the file size of an image be calculated?

A

File size (bits) = image resolution x colour depth

OR

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

62
Q

What is the file size in MB of an 8-bit image that is 2000 pixels wide x 1000 pixels high?

A

8 x 2000 x 1000 = 16’000’000 bits

16’000’000 / 8 = 2’000’000 bytes

2’000’000 / 1000 = 2000 kB

2000 / 1000 = 2 MB

63
Q

What is metadata?

A

Metadata is information stored in an image file which helps the computer recreate it

Without metadata the device would not be able to display the image

64
Q

What does metadata include?

A

File format

Height

Width

Colour depth

Resolution

Time / date

When created / edited

Location

65
Q

How are sounds recorded onto a computer?

A

Sound is recorded by a microphone as an analogue signal

These are sampled and converted into a digital signal

66
Q

What does the following show?

A

A sampled analogue signal

67
Q

How does sampling work?

A

The amplitude of the wave is sampled at regular intervals – each block matches the sample taken

The digital sample, unlike the analogue, isn’t continuous – a lot of data has been lost

The more regular the samples are taken, the less information that is lost – most music is sampled every few milliseconds

68
Q

What is sample rate?

A

Sample rate (frequency) is how many samples are taken per second, measured in Hz

A common sample rate is 44’100 Hz (44.1 kHz)

69
Q

How can the size of a sound file be calculated?

A

File size (bits) = sample rate (Hz) x bit depth x length (seconds)

70
Q

How can the quality of a sound file be changed?

A

Increasing the sample rate means the analogue recording is sampled more often, matching the original sound more closely (better quality)

Increasing the bit-depth means the digital sample picks up quieter sounds even if they’re happening at the same time as louder sounds – again, making the original analogue sound more closely

71
Q

What happens when the sample rate or bit-depth increases?

A

The file size increases

72
Q

Why is compression useful?

A

Smaller files take up less storage space

Streaming / downloading is quicker and requires less bandwidth

Services with restrictions (e.g. email) allows content to be sent which might otherwise have been blocked

73
Q

What are the two types of compression and what are their key attributes?

A

Lossless – the file is made smaller, temporarily removing data to store the file, then restoring it to its original state. No data is lost

Lossy – the file has data permanently removed, limiting the number of bits the file needs

74
Q

What type of compressions are shown in the following image?

A

The image at the top is lossless compression – when reverted, it retains all the data

The image at the bottom is lossy – it has lost some quality

*Lossy allows for greater reduction in size, but at a cost to the quality

75
Q

What are the benefits of Lossy compression?

A

Greatly reduced file size

Take up less bandwidth (download / streaming quicker)

Commonly used

76
Q

What are the negatives of Lossy compression?

A

Loses data – can’t be turned back to original state

Can’t be used on text or software as data cannot be lost for these

Worse quality (though can be unnoticeable)

77
Q

What are the benefits of Lossless compression?

A

Data only removed temporarily – no reduction in quality

Can be decompressed to return to the original state

Can be used on text and software files

78
Q

What are the negatives of Lossless compression?

A

Only a slight reduction in file size is possible

E.g. a lossless song may be compressed to 30MB whilst a lossy compression could get to around 5MB

79
Q

Give some examples of Lossy compression

A

MP3 (audio)

AAC (audio)

JPEG (image)

80
Q

Give some examples of Lossless compression

A

FLAC (audio)

TIFF (image)

PNG (image)

Computer Science (8 decks)

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