Section 3 Data Representation Flashcards
what is a natural number ?
a whole number that is used for cointing
what is a rational number?
any value that can be expressed as a ratio or a fraction
what is an irrational number?
a number that can not be expressed as a ratio or a fraction
what is an ordinal number ?
decsribes the numerical position of objects
why are hexadecimals used ?
as a shorthand binary since it is simple to represent a byte in just 2 digit
they are easier to remeber compared to a 8 bit sequence
what is a byte?
8 bits
what is ASCII
Americamn Standard Code for Information Interchnage
a way of representing letters, numbers and symbols as binary
what is unicode
a way of representing data using 16 bit binary compared to the 8 bit ascii
what are partity bits?
a parity bit is an additional bit that is used to check that the other bits transmitted are likely to be correct
what is majority voting?
this is a system that requires each bit to be sent 3 times. if a bit is flipped erroneously during transmission over a noisy line, the recipient computer would use the majority rule and assume that the two bits that have not chnaged were therefore correct
what is a check digits?
it is an additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission.
what are the rules for binary addition?
0+0 = 0 1+0 = 1 1+1 = 0 ( carry the 1) 1+1+1 = 1 ( carry the 1)
what is an overflow ?
this is when the result of the addition is greater than 255, and an over flow error occurs where a carry from the most significant bit requires a ninth bit
what is unsigned binary?
unisgned representation of binary can only represent positive numbers
what is signed bianry?
can represent both positive and negative numbers
how do you perform twos compliment?
- write out the positive intergrer in normal binary
- flip all of the bits ( turn the 1s into 0s and turn the 0s into 1s)
- add 1
example : -5 00000101 11111010 11111011
fixed point binary
0.5 = 0.1
0.25 = 0.01
0.125 = 0.001
0.0625 = 0.0001
etc
what is a bitmap image?
an image that contains many picutr elements or pixels , that make up the whole image.
what is resolution?
width in pixles * height in pixels
what is resolution sometimes expressed as ?
PP1 = Pixels Per Inch
or
DPI = Dots Per Inch
what is the colour depth?
the number of bits that determine the number of combinations
what is metadata?
data about data additional details that are stored with the image such as : -width -height -colour depth
What are vector graphics ?
vector images are made up of geometric shapes / mathematical equatoions and objects such as lines , curves , arcs and polygons
Vector Graphics vs Bitmap graphics
- vectors will usually have a smaller sile size
- vectors will scale perfectly
- vectors transmit and load faster
what is the sampling rate ?
the frequency with which you record the amplitude of sound
how many readings u take per specific time interval
Calculating sound sample sizes
number of samples per second * the number of bits per sample * the legnth of the sampe in seconds
what is an analouge signal ?
a continuous signal which represents physical measurements
what is a digital signal ?
discrete time signals generated by digital modulation
examples of continuous siganls ?
- human voice
- tape recorder
- analouge watch
example of digital signals ?
computers
cds
dvds
digital watch
how do we quantify analouge sound
continuous varying quantities are measuered
how is a digital signal quantified ?
quantities are counted rather than measured
analouge to digital conversion
- a microphone convertsthesound energy into electrical energy
the analouge to digital converter sampels the analouge data at a given frequency, measuring the amplitude of the wave at each point - then converts this into a binary value according to the resolution
what is frequency ?
something that us determined by the speed of oscillation or vibration of a wave
what is nyquists theorem?
in order to produce an accurate recording the sampling rate msut be doubled that of the highest frequency in the original signal
what is lossy compresion?
this is when non essential informtion/ data is remved
what is loseless compression?
records a pattern in data. using these patterns the computer can reverse the proceduer and reassemble an image
what is rle?
Run legnth encoding , records a pixles value and the number of times it repeats
what is encryption?
encryption is the transformation of data from one form to another to prevent an unauthroised third party from being to be able to understand the data
what is caeser cipher ?
this is a type of substitution cipher and works by shifiting the letters of the alphabet along by a given number of characters
what is vernam cipher ?
implementation of a class of ciphers known as one time pad ciphers . offers perfect security if used properly
