Data Representation Flashcards
What are natural numbers?
Set of numbers containing all positive whole numbers and zero.
Used to count hoe many of an item you have
What are integer numbers?
Set of whole numbers positive and negative, including zero
What are rarional numbers?
Can have fractional part, positive negative and zero. Can be written as fraction or decimal
What are irational numbers?
Cannot be weitten as a fraction
Pi, squared, cubed etc
What are real numbers?
All possible real world quantities - everything
What are ordinal numbers?
Integers used to describe numerical positions of objects in relation to others.
What type of numbers would be used for counting and for measuring
Counting - natural
Measuring - real
What is Character code?
Decimal digit used to represent a character - A - Z represented by 1 - 26
If used by a computer, binary representstion would be used.
What is ASCII
American Standard Code for Information Interchange.
Introduced 1963, uses 7 bits to represent 128 diff characters including alphabet and some symbols
What is Unicode?
Introduced 1991 and allows wide range of alphabets. Uses between 8 and 48 bits (1 - 6 bytes) per character - larger variety than ASCII
What are parity bits?
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.
What are the two types of parity bit?
Odd and even parity
Even - value chosen, make total number of 1’s equal.
Odd - adds parity bit to make data odd.
What is the major issue with parity bits?
If even number of bits are chamged, no error will be detected.
What is majority voting?
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.
What are checksums?
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
What are check digits?
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.
What is the difference between analogue and digital?
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.
Explain analogue / digital conversion.
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.
What is resolution of an image?
Number of dots per square inch (dot = pixel).
- can also refer to number of pixels in an image.
What is colour depth?
Number of bits assigned to a pixel.
2^how many bits assigned.
How do you calculate storage required for bitmap images?
Number of pixes (height x width) × colour depth
What are vector graphics?
Images represented by geometric objects and shapes. Properties of vector stored in list.
Vector graphics vs bitmapped images
Vector:
- scaled without loosing quality
- well suited to logos, not photos
- use less storage - stored information for shape, not pixel.
What is the sampling rate?
Number of samples per second (hertz)
What is sample resolution?
Number of bits allocated to each sample.
Higher sample resolution, higher file size.
How do you work out size of sample?
Duration of sample (s) x sample rate x sample resolution
What is Nyquist Theorem
Sampling rate of audio must be atleast twice the frequency of the sound.
What is MIDI
Musical Instrument Digital Interface
Stores sound as series of event messge. Series of instructions to replicate a piece of music
What are the event messages in MIDI?
- duration of note
- instrument of note played
- volume
- if note should be sustained
What are the advantages of MIDI?
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.
Compare lossy to lossless
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.
What is Run Length Encoding (RLE)?
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.
What is dictionary-based methods.
Dictionary containing repeated data is appended to file. Birmap image -> dictionary of the row, not individual pixel.
What is encryption?
Scrambling data to make it unreadable if intercepted. Unencrypted text - plaintext. Encrypted - cyphertext.
How do ceasar ciphers work?
Encrypt data by replacing characters. Two types: shift and substitution ciphers.
