Unit 3 - Data representation

Question 1

What are natural numbers?

Answer 1

Natural numbers are integers greater than 0.

Question 2

What are ordinal numbers?

Answer 2

The numbers indicating order of occurrence (1st, 2nd, 3rd, etc.)

Question 3

Advantages of using hexidecimal:

Answer 3

• A hexadecimal value is much easier to read and
  remember than a string of binary digits
• It is quicker to write or type, since a hex digit takes
  up only one character, not four
• There is less chance of making an error when typing
  hex characters than a string of 1s and 0s
• It is very easy to convert to and from binary

Question 4

How many possible binary codes does ASCII allow for?

Answer 4

256

Question 5

What are the first 32 characters in the ASCII table?

Answer 5

The first 32 characters are all control characters, such as backspace.

Question 6

How many characters in the ASCII table are control characters?

Answer 6

The first 32 characters are all control characters.

Question 7

How many bits make up the characters in Unicode?

Answer 7

Either 16 or 32 bits.

Question 8

How are parity bits used?

Answer 8

Parity bits are used in error detection. When a byte of data is sent, a parity bit is set to a 1 or a 0 to make the total numbers of 1s in the byte either even or odd depending on the machine.

Question 9

How does majority voting work?

Answer 9

Majority voting is a method of error detection that requires each bit of data being sent three times. From the three bits, a 1 or 0 is chosen based on which one appears more.

Question 10

What is a checksum and what is its purpose?

Answer 10

A checksum is an error checking algorithm that can be applied to a packet of data. The algorithm is applied to the packet to calculate a check digit, which is transmitted with the packet. Upon arrival, the same algorithm is applied to make sure the same check digit is obtained.

Question 11

How does capturing an image using a digital camera work (ignoring colour)?

Answer 11

The image is broken up into a grid of pixels and light sensors are used to detect the intensity/brightness at each pixel. These measurements are converted into a binary code using an analogue-to-digital converter.

Question 12

How does a digital camera recognise colour?

Answer 12

Each pixel of the image is mapped from a set of filters (red, green and blue). The intensity of the individual filters can be used to calculate the amount of their respective wavelength of light.

Question 13

What electrical component is used to convert light sensor measurements into binary codes?

Answer 13

An analogue-to-digital converter.

Question 14

How are bit-mapped graphics represented.

Answer 14

They are represented by a grid of pixels, each holding a colour value.

Question 15

What are the differences between analogue and digital data? (discrete or continuous?)

Answer 15

Analogue data is continuous by nature; the distance between two points would be analogue since you can forever increase the accuracy of measurement… kind of. Discrete data is much more definitive; a byte is discrete because the potential numbers it represents are fixed.

Question 16

What is meant by the sample resolution of an analogue signal?

Answer 16

The sample resolution is the number of bits used to record each measurement.

Question 17

If a recording took a sample every S seconds with a resolution of R over a time of T, what would the resultant file size be? (expressed in terms of S, R, T)

Answer 17

File size = R * T * 1/S

Question 18

What does the Nyquist Theorem state?

Answer 18

When sampling a signal, the sampling frequency must be greater than twice the frequency of the input signal so that the reconstruction of the original image will be as close to the original signal as possible.

Question 19

What does MIDI stand for and how is it different to traditional recording methods?

Answer 19

MIDI (Musical Instrument Digital Interface) creates sounds as requested by software instead of translations of real instruments.

Question 20

How could lossy compression be used for an audio file?

Answer 20

Lossy compression removes the sounds in the frequency ranges that humans can’t perceive. It may also remove quieter notes that are played at the same time as louder ones.

Question 21

Give an example of lossless compression and how it works (spoiler: it starts with R).

Answer 21

RLE (Run Length Encoding) notices consecutive patterns of the same data and shortens them into what in English is “3x data” instead of “data + data + data”.

Question 22

Give an example of lossless compression and how it works (spoiler: it starts with a D).

Answer 22

Dictionary compression spots regularly occurring data and stores that data in a dictionary. The data within the main section of the file is then replaced to refer to the dictionary.

Question 23

How can frequency analysis be used to break simple encryption?

Answer 23

Some letters in the alphabet, such as “S”, are much more common than others. Counting how often a certain letter appears in an encrypted document can narrow which letters it could be. This only works against garbage encryption such as Caesar cipher.

Question 24

How does the Vernam cipher work?

Answer 24

A completely random “one-time pad” is generated that is greater than or equal to the text in length. The pad is shared securely and a XOR operation is applied to every pair of data bits.

Question 25

What is the symbol for a kibibyte and how many bits does it contain?

Answer 25

KiB holding 1024 bits.