Data Representation

Question 1

How many inputs and outputs do NOT gates have?

Answer 1

1) one input

2) one output

Question 2

Put these units in order of size (smallest to largest):

Terabyte, Byte, Kilobyte, Gigabyte, Megabyte

Answer 2

Byte, Kilobyte, Megabyte, Gigabyte, Terabyte

Question 3

Convert 17 (decimal) to binary.

Answer 3

10001

Question 4

Convert 17 (decimal) to hexadecimal.

Answer 4

11

Question 5

Convert 0011 1000 (binary) to decimal.

Answer 5

56

Question 6

What effect do left and right shifts have on binary numbers?

Answer 6

1) left shifts multiply a binary number. For every place shifted left, the number is doubled
2) right shifts divide a binary number. For every place shifted right, the number is halved

Question 7

Convert 1001 1111 (binary) to decimal.

Answer 7

159

Question 8

Convert 1001 1111 (binary) to hexadecimal.

Answer 8

9F

Question 9

Convert 10 1011 (binary) to decimal.

Answer 9

43

Question 10

Convert 10 1011 (binary) to hexadecimal.

Answer 10

2B

Question 11

Convert 4A (hexadecimal) to decimal.

Answer 11

74

Question 12

Convert 4A (hexadecimal) to binary.

Answer 12

1001010

Question 13

Convert 75 (hexadecimal) to decimal.

Answer 13

117

Question 14

Convert 75 (hexadecimal) to binary

Answer 14

1110101

Question 15

Convert 148 (decimal) to binary.

Answer 15

10010100

Question 16

Convert 148 (decimal) to hexadecimal.

Answer 16

94

Question 17

Convert 240 (decimal) to binary.

Answer 17

11110000

Question 18

Convert 240 (decimal) to hexadecimal.

Answer 18

F0

Question 19

Convert BD9 (hexadecimal) to decimal.

Answer 19

3033

Question 20

Convert BD9 (hexadecimal) to binary.

Answer 20

101111011001

Question 21

Encode this string using run-length encoding:

PPPPQQRRRSSSSSSPPPPPQQQ

Answer 21

(4,P), (2,Q), (3.R), (6,S), (5, P), (3, Q)

Question 22

Calculate the number of bits needed to store this string if it was encoded with ASCII:
PPPPQQRRRSSSSSSPPPPPQQQ

Answer 22

23 X 8 = 184 bits

Question 23

Calculate the number of bits needed to store this string if it was encoded with huffman coding:
PPPPQQRRRSSSSSSPPPPPQQQ

Answer 23

9 + 15 +9 +12 = 45 bits

Question 24

Calculate the number of bits needed to store this string if it was encoded with run-length encoding (if each data pair used 2 bytes):
PPPPQQRRRSSSSSSPPPPPQQQ

Answer 24

8 x 2 x 6 = 96 bits

Question 25

Why do programmers prefer hexadecimal over binary and decimal?

Answer 25

1) it's simpler to remember large numbers in hex - they're far shorter than binary numbers 2) due to hex numbers being shorter, there's less chance of input errors 3) it's easier to convert between binary and hex than binary and decimal

Question 26

What is the definition of a character set?

Answer 26

A collection of characters that a computer recognises from their binary representation

Question 27

What are the four types of characters that are included in a character set?

Answer 27

1) uppercase letters 2) lowercase letters 3) digits 4) symbols

Question 28

What are the two main character sets?

Answer 28

1) ASCII | 2) Unicode

Question 29

Define the term 'pixel'.

Answer 29

One of the individual units that that make up an image

Question 30

Define the term 'bitmap'.

Answer 30

An image made up of pixels

Question 31

Define the term 'colour depth'.

Answer 31

The number of bits used for each pixel

Question 32

Define the term 'image resolution'.

Answer 32

The number of pixels in the image

Question 33

What are the effects of choosing a greater image resolution or colour depth for an image?

Answer 33

Using a greater image resolution or colour depth means that there are more bits in the image. This can give a higher-quality image, but also increases the file size

Question 34

How does audio sampling work?

Answer 34

1) sound is recorded by a microphone as an analogue signal 2) the analogue signals are converted into digital data by analogue to digital converters so that computers can read and store sound files

Question 35

Define the term 'sample rate'.

Answer 35

How many samples you take in a second

Question 36

What happens when you increase the sample rate?

Answer 36

Increasing the sample rate means the analogue recording is sampled more often. The sampled sound will be better quality and will more closely match the original recording. However, increasing the sample rate will increase the file size

Question 37

Define the term 'sample resolution'.

Answer 37

The number of bits available for each sample

Question 38

What happens when you increase the sample resolution?

Answer 38

Increasing the sample resolution means the digital file picks up quieter sounds, even if they're happening at the same time as louder ones. This will also result in a sampled sound that is closer to the quality of the original recording. However, increasing the sample resolution will increase the file size

Question 39

Why might you want to compress data?

Answer 39

1) smaller files take up less storage space on a device 2) streaming and downloading files from the internet is quicker as they take up less bandwidth 3) it allows web pages to load more quickly in web browsers 4) email services normally have restrictions on the size of the attachment you can send - compressing the file allows you to send the same content with a much smaller file size

Question 40

What is the difference between lossy compression and lossless compression?

Answer 40

1) lossy compressionn works by permanently removing data from the file - this limits the number of bits the file needs and so reduces its size 2) lossless compression makes the file smaller by temporarily removing data to store the file and then restores it to its original state when it's opened

Question 41

Why might you want to use lossy compression?

Answer 41

1) greatly reduced file size, meaning more files can be stored 2) takes up less bandwidth so can be downloaded and streamed more quickly 3) commonly used - lots of software can read lossy files

Question 42

Why might you want to use lossless compression?

Answer 42

1) data is only removed temporarily so there is no reduction in quality - the compressed file should look or sound like the original 2) can be decompressed - turned back into the original 3) can be used on text and software files

Question 43

What is the formula used to work out how many bits an image will take up?

Answer 43

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

Question 44

What is the formula used to calculate the size of a sound file?

Answer 44

file size (in bits) = sample rate (in Hz) x sample resolution x length (in seconds)