3.3 Data Representation

Question 1

What is binary?

Answer 1

A number system that uses 1s and 0s

Question 2

Why is Binary used?

Answer 2

Because it has two states (1 and 0) which can represent on/off, true/false, open/closed for example

Question 3

What is binary used for in a computer?

Answer 3

Computers are based on circuits with switches that are either open or closed. The binary number system can therefore be used to change the switches because it also has two states of 1 and 0

Question 4

What is the Most Significant Bit (MSB)?

Answer 4

Bit furthest to the left with the largest place value

Question 5

What is the Least Significant Bit (LSB)

Answer 5

Bit furthest to the right with the lowest place value

Question 6

How to work out the number of binary representations?

Answer 6

2^n

Question 7

How to work out the largest number in a certain number of bits?

Answer 7

2^n - 1
n is the number of bits

Question 8

What are the different sizes of storage?

Answer 8

bit (b) = 0 or 1 or 1/8 byte
nibble = 4 bits or 1/2 byte
byte (B) = 8 bits
kilobyte (KB) = 1 000 bytes
megabyte (MB) = 1 000 000 bytes
gigabyte (GB) = 1 000 000 000 bytes
terabyte (TB) = 1 000 000 000 000 bytes

Question 9

What is an overflow error?

Answer 9

The result of the addition is too large to store in 8 bits i.e the result is greater than 255

Question 10

How do you convert from hexadecimal to denary?

Answer 10

16 |1 |
3 |B |
(3 x 16)| + 11 |= 59

Question 11

How do you convert from denary to hexadecimal?

Answer 11

229 / 16 = 14 (E) remainder 5 = E5

Question 12

Who uses hexadecimal?

Answer 12

Humans - programmers, Computer Scientists
Computers ALWAYS use binary

Question 13

Why use hexadecimal?

Answer 13

• Easier to remember a hex number than a binary number
  -Because it is a more compact form -
  four binary digits are represented with
  a single hex value
  -Therefore it is less likely that
  errors are made
• It is easy to convert between hex and binary

Question 14

What are the effects of shifts?

Answer 14

Direction| Places | Outcome

Left | 1 | x 2
Left | 2 | x 4
Left | 3 | x 8
Left | 4 | x 16

Right | 1 | / 2
Right | 2 | / 4
Right | 3 | / 8
Right | 4 | / 16

LEFT = multiply
RIGHT = divide

Question 15

What are the effects of a right shift?

Answer 15

Loss of accuracy as bits may be lost

Question 16

What are the two main character sets used today?

Answer 16

ASCII
Unicode

Question 17

What is a pixel?

Answer 17

The smallest identifiable part of an image

Question 18

Calculating image file size

Answer 18

in bits
= width x height x colour depth
in bytes
= width x height x colour depth / 8

Question 19

What is metadata?

Answer 19

Data in data - information other than the actual image data is also stored with a file

Question 20

What is included in the metadata?

Answer 20

Colour Depth
Height and width of image in pixels
Date created
Author
GPS - where it was taken

Question 21

Why is metadata necessary?

Answer 21

Allows the binary data to be correctly interpreted

Question 22

How is a computer able to store sound?

Answer 22

The analogue wave is digitised by repeatedly measuring and recording the sound wave

Question 23

Difference between analogue and digital waves

Answer 23

analogue - continuous waves
digital - signals are discrete

Question 24

What does an Analogue to Digital Converter do?

Answer 24

Takes an analogue sound waves as an input and converts it to a digital signal.
Done by a Sound card

Question 25

What does a Digital to Analogue Converter do?

Answer 25

Takes the digital signal and converts it to an analogue sound wave as an output.
Done by a Sound card

Question 26

What is a sound sample?

Answer 26

A sound sample is a measurement of amplitude (height) of a sound wave at a given time

Question 27

What is the sampling rate?

Answer 27

The sampling rate is the number of samples taken per second.
It is measured in hertz (Hz):
- 1Hz = 1 sample per second

Question 28

What is the sample resolution (or bit depth)?

Answer 28

The number of bits used to record each measurement is known as the sample resolution or bit depth

Question 29

What is the formula for calculating sound file sizes?

Answer 29

File size (bits) = sampling rate (Hz) × resolution × duration (seconds)

Question 30

What frequency can humans hear sounds?

Answer 30

20 - 20,000 Hz

Question 31

What is Lossy compression?

Answer 31

Permanently removes parts of the file
The lost piece of data can never be restored

Question 32

What is Lossless compression

Answer 32

Reduces the file size when compressed but does not lose any information

Question 33

What is compression?

Answer 33

Compression is the name given to the algorithms which reduce file size.

Question 34

What is decompression?

Answer 34

Decompression is the process where compressed data is restored to its original format

Question 35

What is Run Length Encoding (RLE)?

Answer 35

RLE uses frequency/data pairs to encode each run length of the same coloured pixel

Question 36

What does Huffman coding analyse?

Answer 36

Frequency with which characters in a body of text are used

Question 37

Benefits of compression

(you don’t need to know them all)

Answer 37

-Faster transmission time-
Smaller file size = fewer bits = faster transmission time

-Reduces network traffic-
Smaller fie size = less network traffic = fewer packet collisions

-Video Streaming-
Data can be sent as fast as it can be played

-Detailed webpages-
More extensive content can be displayed on webpages as it will download quicker

-Reduced storage space-
Files do not take up as much space on the disk/server