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AQA Computer Science > Fundamentals Of Data Representation > Flashcards

Fundamentals Of Data Representation Flashcards

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1
Q

Natural numbers (N)

A

Don’t represent negative
Represents whole numbers
(0, 1, 2, 3)

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2
Q

Integer numbers (Z)

A

Represent both whole and negative numbers

-3, -2, -1, 0, 1, 2

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3
Q

Rational numbers (Q)

A

Can be written as fractions

( 7/1) =7

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4
Q

Irrational numbers

A

Cannot be written as a fraction

pie, root 2

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5
Q

Real numbers (R)

A

Set of all possible real world quantities

Any written number

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6
Q

Ordinal numbers

A

Tells the position of a list of numbers
{a, b, c, d}
A is the first position

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7
Q

Decimal

A

67(10)

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8
Q

Binary

A

10011011(2)

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9
Q

Hexadecimal

A

AE(16)

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10
Q

Bit

A

Fundamental unit of information

0, 1

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11
Q

Byte

A

8 bits

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12
Q

2^n

A

Number of different values

3 bits = 2^3 = 8 different ways

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13
Q

Binary prefixes

A

Kibi - 2^10
Mebi - 2^20
Gibi - 2^30
Tebi- 2^40

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14
Q

Decimal prefixes

A

Kilo - 10^3
Mega - 10^6
Giga - 10^9
Tera - 10^12

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15
Q

Signed numbers

A

Represents positive and negative numbers
(1001001111)
First digit is 1

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16
Q

Unsigned

A

Does not represent negative numbers
(0001100111)
First digit is 0

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17
Q

Minimum and maximum value for a given number of bits in unsigned binary

A

0 and 2^n - 1

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18
Q

Why can fixed point and floating point representation of decimal numbers be wrong

A

There is a rounding error

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19
Q

Advantage of floating point

A

Provides a large range

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20
Q

Disadvantage of floating point

A

Rounds off large numbers which is time consuming

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21
Q

Advantage of fixed point

A

Numbers are represented with precision

e.g. when money is involved

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22
Q

Disadvantage of fixed point

A

Provides a limited range

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23
Q

Why are floating point numbers normalised

A

To increase consistency. If each number is represented always by the same bit pattern comparisons would become easier

24
Q

Overflow and where it occurs

A

When the result of addition or subtraction goes beyond range

+ and + = -
- and - = +

25
Q

Underflow

A

When the result of addition or subtraction is less than the range

26
Q

Why is vernam cypher considered to be perfect

A

Harder to crack

Nothing can’t be learnt about the plaintext from the cypher text

27
Q

Why is caeser cipher easily cracked

A

There are only 25 possible keys which comes to process of elimination

28
Q

Compare vernam cipher to other cyphers that depend on computational security

A

Vernam cipher is the only one to be mathematically secure whereas other ciphers can be broken given enough cipher text and time

29
Q

Encryption

A

Using an algorithm to convert a message into cipher text

30
Q

Advantage of MIDI

A

More compact

Easy to modify

31
Q

Advantage and disadvantage of lossless

A

Files can be reproduced exactly as it was in the beginning with no loss in quality but still result in a large file size
No redundant data is lost during the compression process

32
Q

Advantage and disadvantages of lossy

A

Files are reduced significantly more than lossless but has a loss in quality

33
Q

Principle of dictionary based compression

A

Variable length strings of data are represented by single tokens
A dictionary is formed using the tokens as the key
The strings of symbols are used as the entries

34
Q

RLE

A

compresses data by reducing repetitive and consecutive data called runs. Runs of data are stored as a single data value and count rather than the original run

35
Q

Why are images and files compressed

A

To reduce files which helps streaming or downloading files.

36
Q

Compressing text files

A

Smaller and faster to send wireless networks

37
Q

Purpose of midi

A

To easily edit files and exchange data?

38
Q

Nyquists theroem

A

Sample rate is double the highest frequency in the original sound

39
Q

Sample rate equation

A

Size / (sample resolution x time)

40
Q

Sample resolution

A

Number of bits per sample

41
Q

Sample rate

A

Number of samples taken per second

42
Q

Compare bitmap graphics to vector graphics

A

Bitmaps are made up of pixels while vector graphics are created using a mathematical formula

Vector takes up less storage than bitmap due to bitmap being made from pixels.

43
Q

Why is Unicode good

A

Can represent characters from languages all around the world

44
Q

Difference between analogue data and digital data

A

Analogue is continuous data

Digital is stored as binary

45
Q

ADC process

A

The analogue signal is sampled at fixed time intervals

The amplitude of a signal wave at each sample point is measured which is then coded in binary

46
Q

Parity bit

A

A method of checking binary codes by counting the number of 0s and 1s in code

47
Q

Majority voting

A

Method of checking for errors by producing the same data several times and checking it is the same each time

48
Q

Check digit

A

A digit calculated using an algorithm and is generated using other digits in a sequence

49
Q

Ascii

A

Binary coding system for characters and numbers

50
Q

Unicode

A

Binary coding system that includes international characters

51
Q

Most common use for a dac

A

To convert a digital audio signal to an analogue signal

52
Q

Colour depth

A

Number of bits stored for each pixel

53
Q

Resolution

A

Number of dots per inch where a dot is a pixel

54
Q

Bitmapped graphic

A

An image made up of individual pixels

55
Q

Size of pixel

A

Width of images x height of images

56
Q

Storage requirements

A

Size in pixels x colour depth

AQA Computer Science (16 decks)

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