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Computing > 05 Data Representation > Flashcards

05 Data Representation Flashcards

1
Q

What are natural numbers?

A

Any number from 1-9

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2
Q

What are integers?

A

Any positive or negative whole numbers

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3
Q

What are rational numbers?

A

Values that can be expressed as fractions

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4
Q

What are irrational numbers?

A

Numbers that cannot be expressed as fractions
Decimal values that are endless
(Pi)

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5
Q

What is a real number?

A

Any rational or irrational number

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6
Q

What are ordinal numbers?

A

Numbers that describe the position that values appear in

1st,2nd

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7
Q

What are the binary and denary number systems?

A

Binary is base 2 with digits 0 and 1

Denary is base 10

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8
Q

How do you convert from denary to binary?

A

Draw the table from 128 to 1 and add up

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9
Q

What is hexadecimal?

A

Base 16 which uses 1-9 then from A=10 B=11 and so on

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10
Q

What are the rules of place value for hexadecimal?

A

Last digit must be times by 16^0 and next must be times by16^1 and so on

E.g

F5 = (16^1 x 15) + (16^0 x 5)
= 16x15 + 1x5
=240 + 5
=245

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11
Q

How do convert denary to hexadecimal?

A

Divide the number by 16 and add the remainder

Example: 2468

2400 ÷ 16 = 154
remainder 4

154 ÷ 16 = 9 remainder A

9 ÷ 16 = 0 remainder 9

2468 in denary is 9A4 in hex

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12
Q

How do you convert from binary to hexadecimal?

A

Split the binary number in halves of 4 bits and convert them to hex

11011000

8421 8421
1101 1000

13 8

D8

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13
Q

How do you convert from hexadecimal to binary?

A

Turn each digit into 4 bit binary

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14
Q

Why use hexadecimal?

A

Hexadecimal is easier to read than binary
Quicker to write
Less chance of making an error
Used to define colours, in MAC addresses, machine code and assembly language
Easy to convert to and from binary

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15
Q

How do you add binary numbers?

A 
0+0 = 0
1+0 = 1
1+1 = 0 carry 1
1+1+1 = 1 carry 1
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16
Q

What is overflow error?

A

When the result of addition is too large for the number of bits the computer can work with

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17
Q

How do you multiply binary numbers?

A

Same as decimal multiplication where u multiply everything by last digit then add 0 to end and use second digit

0x0 = 0
0x1 = 0
1x0 = 0
1x1 = 1
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18
Q

How are negative numbers represented in binary?

A

Using two’s complement

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19
Q

How do you calculate two’s complement?

A

Flip all of the bits and add 1 to the end

E.g.

-3 = 11111101
3 = 00000011
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20
Q

What is the range of values that can be counted in binary and using two’s complement?

A

Binary = 2^n-1

Two’s complement = -(2(^n-1)) … 2(^n-1) - 1

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21
Q

How do you subtract two binary numbers?

A

Turn one into a negative using two’s complement and add them together

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22
Q

How do you show binary fractions?

A

Use bits to the right as fractions

Instead of 128 64 32 16 8 4 2 1

It would be 8 4 2 1 1/2 1/4 1/8 1/16

They are negative powers of 2 (2^-1, 2^-2)

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23
Q

What is a fixed point binary value?

A

It uses a specified number of bits where the binary point is fixed

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24
Q

How many bits is a byte?

A

8 bits

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25
Q

How many bytes are in one kilo, mega, giga and tera byte?

A 
Kilo = 10^3 = 1000
Mega = 10^6 = 1,000,000
Giga = 10^9 
Tera = 10^12
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26
Q

How many bytes are in one kibi, mebi, gibi and tebi byte?

A 
Kibi = 2^10
Mebi = 2^20
Gibi = 2^30
Tebi = 2^40
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27
Q

What is ASCII?

A

American Standard Code for Information Interchange

Encodes symbols found in the English alphabet

Different binary values for uppercase, lowercase and punctuation, space, numbers and special characters.

28
Q

What is Unicode?

A

Standardises encoding of characters from all languages as ASCII only worked in English

Can be 16 or 32 bits

29
Q

What is a transmission error and why might it occur?

A

When data doesn’t arrive in the same format it was sent

Electrical interference
Power surges
Synchronisation issues
Wear and tear on cable or connectors

30
Q

What might a transmission error cause?

A

It can cause bits to flip

31
Q

What are four ways of error detection?

A

Parity Bits
Majority Voting
Check Digits
Check Sums

32
Q

What happens when an error is detected?

A

The data cannot be corrected so a request to resend data is invoked

33
Q

What are parity bits?

A

One bit in the data is used as a parity bit to show odd or even
The number of 1s must be odd for odd parity and even for even parity

34
Q

What is majority voting?

A

Each bit is sent three times and the majority rule is applied
E.g. if there are two 1s and one 0 then the bit will be 1

35
Q

What is a check digit?

A

An additional digit at the end of a string designed to check for mistakes

36
Q

What is a checksum?

A

A total sum of all the bytes is calculated using an algorithm and is sent with the data
The receiver then calculates the checksum and works out whether the value was right

37
Q

What is digital and analogue data?

A

Digital is in a format a computer can understand

Analogue can be measured to any degree of accuracy

38
Q

How is an image captured?

A

A light sensor measures intensity of colour in each pixel

This is converted into a binary code using an an analogue-to-digital convertor

39
Q

What are the types of bitmap file?

A 
BMP
JPG
GIF
PNG
TIF
40
Q

What is resolution and how is it worked out?

A

Number of Pixels used to make up a bitmap image

Width x height

41
Q

What happens when an image is made bigger or smaller?

A

The size of each pixel grows or shrinks

When made bigger this decreases quality

42
Q

What is bits depth or colour depth?

A

Allows more colour combinations

Worked out by 2 to the power of number of bits

43
Q

How are colour values expressed?

A

In hexadecimal with RGB values as binary would take up too much space

44
Q

How is image file size calculated?

A

Number of pixels (resolution) x colour depth

45
Q

What is metadata?

A 
Data about the image stored in the same file
E.g. 
Date
Width and height 
Colour depth
GPS location
46
Q

What are ADCs and DACs?

A

ADCs - Analogue to Digital converters (Microphones)

DACs - Digital to Analogue converters (Speakers)

47
Q

How does analogue to digital and digital to analogue conversion work?

A

Recorded via amplifier (sampled at set intervals)
Each sample is quantised to measure height
Integer value is stored as binary
Reverse happens for digital to analogue

48
Q

What is sampling and sampling rate?

A

An analogue signal is measured at regular periods.
Amplitude is sample resolution (audio bit depth)
Sampling rate - (Hertz) Number of samples taken in one second

49
Q

How does sampling rate affect detail and file size?

A

Higher sampling rate = more detail = higher file size

50
Q

How do you work out sound file size?

A

File size =

sample rate x resolution x length in seconds

51
Q

What is the Nyquist theorem?

A

Samples must be twice the highest frequency in order to replicate original sound wave

52
Q

What frequencies can the human ear hear?

A

Between 20Hz and 22kHz

53
Q

What is MIDI and what are its benefits and drawbacks?

A

Musical Instrument Digital Interface
Creates synthesised sounds
Reduces amount of data transferred
May not sound realistic

54
Q

What can a sound processor do?

A

Send a timed sequence of event messages to

Synchronise tempo
Control pitch
Change volume
Introduce and silence other instruments in a digital orchestra

55
Q

What are advantages and disadvantages of data transfer?

A

Is usually high speed and accurate

Longer distance means slower speed
Storage space can be limited

56
Q

What does reducing the amount of data do?

A

Data is sent more quickly

Less bandwidth is used as transfer limits may apply
Buffering on audio and video streams is less likely to occur
Less storage is required

57
Q

How does lossy compression work?

A

Non essential data is removed

E.g. different shades of the same colour or frequencies outside of human hearing

58
Q

How does lossless compression work?

A

Patterns in the data and summarised in a shorter format without being removed

Run Length encoding : good for images and sounds

59
Q

What is dictionary compression?

A

Spots regularly occurring data and stores it separately in a dictionary
Good for larger data sets

60
Q

What is Run Length Encoding?

A

Basic method of compression that summarises consecutive patterns
Good for images and sounds

61
Q

What is encryption?

A

A way of making sure data cannot be understood if you don’t possess the means to decrypt it

62
Q

What is a Caesar cipher?

A

Most basic type of encryption

Letters of alphabet are shifted by a consistent amount

63
Q

What is a brute force attack?

A

When every possible key is applied in an attempt to decrypt cipher text

64
Q

What is frequency analysis?

A

Finding letters that are most used like E, T and A to help decrypt the ciphertext

65
Q

What is the vernal cipher?

A

One time pad
Only cipher that is unbreakable (not computer generated)
Key must be truly random and shared with only the recipient and destroyed afterwards

66
Q

How can you decode the message?

A

Performing an XOR operation with the shared key bit by bit

67
Q

Are ciphers completely secure?

A

Ciphers are based on computational security
The keys are determined using a computer algorithm
A key derived from an algorithm, can also be unpicked
Given enough ciphertext, computer power and time, any key (except the one-time pad) can be determined and the message cracked

Computing (5 decks)

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