Data Representation

Question 1

What are natural numbers?

Answer 1

Set of numbers containing all positive whole numbers and zero.

Used to count hoe many of an item you have

Question 2

What are integer numbers?

Answer 2

Set of whole numbers positive and negative, including zero

Question 3

What are rarional numbers?

Answer 3

Can have fractional part, positive negative and zero. Can be written as fraction or decimal

Question 4

What are irational numbers?

Answer 4

Cannot be weitten as a fraction

Pi, squared, cubed etc

Question 5

What are real numbers?

Answer 5

All possible real world quantities - everything

Question 6

What are ordinal numbers?

Answer 6

Integers used to describe numerical positions of objects in relation to others.

Question 7

What type of numbers would be used for counting and for measuring

Answer 7

Counting - natural

Measuring - real

Question 8

What is Character code?

Answer 8

Decimal digit used to represent a character - A - Z represented by 1 - 26

If used by a computer, binary representstion would be used.

Question 9

What is ASCII

Answer 9

American Standard Code for Information Interchange.

Introduced 1963, uses 7 bits to represent 128 diff characters including alphabet and some symbols

Question 10

What is Unicode?

Answer 10

Introduced 1991 and allows wide range of alphabets. Uses between 8 and 48 bits (1 - 6 bytes) per character - larger variety than ASCII

Question 11

What are parity bits?

Answer 11

Singke bit added to transmission that can be used to check for errors. Value is calculated from transmitted data

Parity check occurs when data recirved - if value of bit correlates to correct type of parity bit, transmission is treated as correct. Othereise, retransmitted.

Question 12

What are the two types of parity bit?

Answer 12

Odd and even parity

Even - value chosen, make total number of 1’s equal.

Odd - adds parity bit to make data odd.

Question 13

What is the major issue with parity bits?

Answer 13

If even number of bits are chamged, no error will be detected.

Question 14

What is majority voting?

Answer 14

Each bit is transmitted multiple times - most commonly occuring value is taken to be correct.

When error occurs - majority doesn’t detect error, just corrects it. - no need for retransmission

Volume of data transmitted (timsed by 5) - major downside.

Question 15

What are checksums?

Answer 15

Involves addition to a value determined by data itself

Algorithm used to determine value of checksum based on transmitted data - simple modulo function works.
- repeated by recipient. If it does not match, data is retransmitted

Question 16

What are check digits?

Answer 16

Type of checksum where only a single digit added to data
reduces no. algoritms used to calculate value of check digit - reduces variety of errors method can detect.

Question 17

What is the difference between analogue and digital?

Answer 17

Analogue - continuous with no limits
Digital - discrete, only particulsr values can be taken

Trace of analogue graph - smooth, curves eith sharp peaks
Trace of digital graphs - sharp edges, vertical drops.

Question 18

Explain analogue / digital conversion.

Answer 18

DAC - device reads bit pattern and outputs alternating analogue eletrical current.
Most common use - audio signal -> analogue signal

ADC - convert analogue to digital bit pattern. Takes reading at regular intervals (sampling)
- frequency of sample = hertz - smaples /s
Higher sample rate, better reproduction of signal.

Question 19

What is resolution of an image?

Answer 19

Number of dots per square inch (dot = pixel).
- can also refer to number of pixels in an image.

Question 20

What is colour depth?

Answer 20

Number of bits assigned to a pixel.
2^how many bits assigned.

Question 21

How do you calculate storage required for bitmap images?

Answer 21

Number of pixes (height x width) × colour depth

Question 22

What are vector graphics?

Answer 22

Images represented by geometric objects and shapes. Properties of vector stored in list.

Question 23

Vector graphics vs bitmapped images

Answer 23

Vector:
- scaled without loosing quality
- well suited to logos, not photos
- use less storage - stored information for shape, not pixel.

Question 24

What is the sampling rate?

Answer 24

Number of samples per second (hertz)

Question 25

What is sample resolution?

Answer 25

Number of bits allocated to each sample.
Higher sample resolution, higher file size.

Question 26

How do you work out size of sample?

Answer 26

Duration of sample (s) x sample rate x sample resolution

Question 27

What is Nyquist Theorem

Answer 27

Sampling rate of audio must be atleast twice the frequency of the sound.

Question 28

What is MIDI

Answer 28

Musical Instrument Digital Interface

Stores sound as series of event messge. Series of instructions to replicate a piece of music

Question 29

What are the event messages in MIDI?

Answer 29

• duration of note
• instrument of note played
• volume
• if note should be sustained

Question 30

What are the advantages of MIDI?

Answer 30

Easy manipulation, no loss of quality. Instruments easily changed, notes can be transposed and duration changed.
File size much smaller, and lossless.

Can’t store voices and sometimes sounds synthetic.

Question 31

Compare lossy to lossless

Answer 31

Lossy - reduction in quality and information. No limit to how much it can be compressed.

Lossless - no information or quality loss. Limited to how much it can be compressed.

Question 32

What is Run Length Encoding (RLE)?

Answer 32

Reduces file size by removing replicated information into one occurrence.

1,2,3,3,3,4,5,5,6 -> 1,2,3(3),4,5(2),6

Replaces repeated bit patterns with one pixel value and number of repetitons.

Question 33

What is dictionary-based methods.

Answer 33

Dictionary containing repeated data is appended to file. Birmap image -> dictionary of the row, not individual pixel.

Question 34

What is encryption?

Answer 34

Scrambling data to make it unreadable if intercepted. Unencrypted text - plaintext. Encrypted - cyphertext.

Question 35

How do ceasar ciphers work?

Answer 35

Encrypt data by replacing characters. Two types: shift and substitution ciphers.