Computer Science > Data Representation > Flashcards

Data Representation Flashcards

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1
Q

Natural numbers

A
  • All positive whole numbers and zero
  • Used for counting
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2
Q

Integer numbers

A

All whole numbers, including zero

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3
Q

Rational numbers

A
  • Numbers that can have a fractional part
  • Includes zero
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4
Q

Irrational numbers

A

Numbers that cannot be written exactly as a fraction

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5
Q

Real numbers

A
  • All possible real world quantities
  • All members of irrational, rational, integers and natural numbers are real numbers
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6
Q

Ordinal numbers

A

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

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7
Q

Decimal

A
  • Uses the digits 0 through 9
  • Denoted with subscript 10
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8
Q

Binary

A
  • Uses the digits 0 and 1
  • Can represent high and low currents
  • Denoted with subscript 2
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9
Q

Hexadecimal

A
  • Uses the digits 0 through to 9 followed by the uppercase characters A to F
  • Denoted with a subscript 16
  • Can represent numbers using far fewer digits than binary or even decimal
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10
Q

Bit

A
  • The fundamental unit of information
  • Represents high or low current
  • Can take either of the values 0 and 1
  • The more bits assigned to a number, the more values can be represented
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11
Q

Byte

A

8 bits

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12
Q

Nibble

A

4 bits

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13
Q

Binary prefixes

A

Go up in powers of 2

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14
Q

Denary prefixes

A

Go up in powers of 10

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15
Q

Unsigned binary numbers

A

Can only represent positive numbers

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16
Q

Signed binary numbers

A

Can also represent negative numbers

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17
Q

Range of unsigned binary numbers

A

0 to 2^n - 1

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18
Q

Two’s complement

A
  • The MSB is given a negative place value
  • Has a range of 2^(n-1) to -2^(n-1)
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19
Q

Information coding system

A

The method computers follow to represent characters

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20
Q

Character code

A

A decimal digit used to represent a character

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21
Q

ASCII

A
  • A character encoding system that is used to represent English characters
  • Uses 7 bits to represent 128 different characters
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22
Q

Unicode

A
  • A character encoding system that is used to represent text from all languages (and other symbols)
  • Uses anywhere from 8 to 48 bits per character
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23
Q

Error checking methods

A
  • Parity bits
  • Majority voting
  • Checksums
  • Check digits
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24
Q

Parity bits

A
  • A single bit added to a transmission that can be used to check for errors in transmitted data
  • Can use even or odd parity
  • If an error is detected the computer asks the sender to retransmit the data
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25
Even parity
The parity bit makes the total number of 1s in the transmitted data even
26
Odd parity
The parity bit makes the total number of 1s in the transmitted data odd
27
Issue with parity bits
If an even number of bits are changed during transmission, the error is not detected
28
Majority voting
- Each bit of the data is transmitted multiple times with the most commonly occurring value taken to be correct - Majority voting doesn't just detect errors, it also corrects them
29
Issues with majority voting
- The volume of data being transmitted is increased, increasing the time taken to transmit data - If multiple bits are changed then the transmission can still be incorrect
30
Checksums
- A value is appended to the transmitted data, determined by the data itself - Once received the recipient removes the checksum and carries out a check to ensure the checksum is correct - If the 2 do not match the sender must re-transmit the data
31
Check digits
- An extra digit added to the end of a number that detects errors - It is calculated by performing a mathematical formula based on the other digits
32
Representing data
Computers use bit patterns to represent all forms of data
33
Analogue signals
Can take any values and can change as frequently as required
34
Digital signals
Must always take one of a specified range of values and can only change value at specified intervals
35
Digital to analogue conversion
- Uses a digital to analogue converter - The device reads a bit pattern representing an analogue signal - Outputs an alternating, analogue, electrical current
36
Analogue to digital conversion
- Uses an analogue to digital converter - The device takes a reading of an analogue signal at regular intervals and records the value - Samples are taken at a specific frequency
37
Sampling
The process of measuring the magnitude of an analogue signal at regular intervals
38
Sampling rate
The number of samples taken per second
39
Sample resolution
The number of bits used to store each sample
40
Bitmap graphics
Images made up of many individual pixels
41
Pixels
- The smallest individually addressable point on an image - Has an assigned binary value that determines the color of the pixel
42
Resolution
- Pixels per square inch - Total number of pixels in an image
43
Color depth
- The number of bits assigned to a pixel - n pixels can represent 2^n different colours
44
Metadata
Additional information about an image, e.g date created
45
Vector graphics
- Uses geometric objects and shapes to create images - The properties of each object is stored in a list
46
Vector vs Bitmap graphics
- Vector graphics can be scaled without losing quality - Vector graphics cannot be used for photographs - Vector graphics take less storage space
47
Samples
A measure of an analogue sound wave
48
Sampling rate
Number of samples taken per second
49
Sample resolution
The number of bits allocated to each sample
50
Size of a sound file
duration * sampling rate * sample resolution
51
Nyquist Theorem
The sampling rate must be at least twice the frequency of the signal
52
MIDI
Stores sounds as a series of event messages
53
Event messages
- A representation of an event in a piece of music - e.g duration of a note, instrument played, volume, etc
54
Benefits of MIDI
- Allows easy manipulation without loss of quality - Instruments for each note can be changed - Notes can be transposed - Duration of notes can be altered
55
Drawbacks of MIDI
- Can't store speech - Creates a less realistic sound
56
Data compression
Files are compressed to reduce their size and allow for faster transmission
57
Lossy compression
- Files are reduced in size by reducing quality - There is no limit to the amount of compression that can be applied
58
Lossless compression
- Files are reduced in size whilst keeping all information - There is a limit to the amount of compression that can be used
59
Run length encoding
- A form of lossless compression that removes retreated information - Each run of information is replaced by a single occurrence, followed by the number of times it has been repeated
60
Dictionary-based methods
- Creates a dictionary of repeated data that is appended to the file - The file is reduced in size but the dictionary must also be present
61
Encryption
- The process of converting plaintext into ciphertext in order to prevent unauthorized access - Even if the data is intercepted it is scrambled so cannot be understood
62
Plaintext
The original, readable data
63
Ciphertext
The encrypted, unreadable version of the plaintext
64
Cipher
The algorithm used to perform encryption/decryption
65
Caeser cipher
Encrypts information by shifting each character a fixed number of positions along the alphabet
66
Vernam cypher
- A one-time pad cipher that is mathematically proven to be completely secure - Each character of the plaintext is combined with a character from the key using the XOR operation
67
One-time pad
A random key that is as long as the plaintext, completely random and only used once
68
Computational security
All ciphers other than the Vernam cipher are crackable, but not within a reasonable timeframe - making them sufficiently secure but more practical
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