Unit 5 - Fundamentals of data representation Flashcards
What are natural numbers?
All positive numbers
What are integer numbers?
All positive / negative numbers
What are rational numbers?
All fractional numbers
What are irrational numbers?
Numbers that can’t be written as a fraction
What are real numbers?
All positive or negative value and can include a fractional part
What are ordinal numbers?
Describe the position/placing of an item
What is a parity bit?
a bit set at the transmitting end for error detection
What is a check digit?
Additional digit at the end of a string to check for mistakes in input
What is majority voting?
Majority rule that assumes that if majority bits have not changed it is correct
What are analogue and digital signals?
Analogue - continouus
Digital - discrete
How is analogue converted into digital?
- Sample measured by wave height
- Translated into an integer value
- Then converted and stored digitally as binary value
What is sampling?
Process of converting analogue to digital
What is sample resolution?
The number of bits used to record each measurement
- More bits = higher resolution (better accuracy)
What is sampling rate?
The frequency or number of samples per second
How do you calculate the file size?
File size (Bytes) = sample rate(Hz) x resolution(pixels)x length in seconds
What is Nyquist Theorem?
You must use a sampling rate at double the frequency of the original sound
fs > 2fmax
What is MIDI?
Musical Instrument Digital Interface
- Allows electronic musical instruments to communicate with each other
- Uses less disk space than digital recording
What are event messages?
Sends and receives specific messages to each device
- Duration of note
- Pitch
- Volume change
- Vibrato
- Tempo
What is bitmap resolution?
The number of pixels used to make up a bitmap image
- width x height
What is colour depth?
The number of bits or bytes allocated to represent the colour of a pixel in a bitmap
- storage = resolution x colour depth
What is metadata?
data about data
- date created
- colour depth etc
What does reducing data size do?
- Data sent more quickly
- Less storage required
- Less bandwith used
What is lossy compression?
Non-essential data is
permanently removed
- JPEG & MP3
- Loses original data
What is lossless compression?
No data removed but data is rearranged to be more efficient
- Higher file size
- No loss in quality
What is run length encoding?
Groups together repeated bits
What is dictionary compression?
Spots regularly occurring data and stores it
separately in a dictionary
- Produces additional data for the dictionary itself
What is encryption?
data that cant be understood and needs to be decrypted to be understood
What is Caesar cipher?
An old encryption but Julius Caesar
- realigining alphabet and shifting to encrypt
Disadvantages of Caeser cipher
- Only 25 possible keys
- Only encrypts letters
- Key is constant, so when one match is found, rest will be easily found
What is the Verman cipher (One time pad cipher)?
A key that is only used once to encrypt and decrypt a message and is then discarded
- Truly random
- more or equal length of plain text
- Used XOR logic gates
Why is the Verman cipher ‘perfect security’?
- Truly random
- Never reused
- Must be kept secret
Limitations of Verman cipher
- Key must be more or equal size
- They must be random every time
- Long keys hard to remember
What is two’s compliment
A method of working with signed binary values.
What is fixed point binary?
A way of representing binary fractions
