Data representation Flashcards
Bit
fundamental unit of information in the form of a single 1 or 0
Byte
a group of 8 bits
Nibble
a group of 4 bits
Kibibyte
2^10 bytes
Mebibyte
2^20 bytes
Gibibyte
2^30 bytes
Tebibyte
2^40 bytes
ASCII code
American Standard Code for Information Interchange - code that defines how keyboard characters are encoded into digital strings of ones and zeros
Unicode
symbol that enables most of the languages in the world to be symbolised with a special character identification
Parity bit
an additional bit that is transmitted as part of a byte to make the total number of ones odd (odd parity) or even (even parity) - data transmitted can be checked by counting the number of ones in a character code to check that there have been no errors during transmission
Majority voting
system which requires each bit to be sent three times - if a bit value is flipped incorrectly during transmission over a heavy trafficked line, receiving computer uses majority rule and assumes the two bits have not changed and were therefore correct
Checksums
involve adding a mathematical algorithm to the transmitted data; block of (transmitted) data used to create a checksum value which is transmitted with the block - same algorithm is applied to the block after transmission and if the two checksums match, the transmission is considered successful
Check digits
additional digit at the end of a string of other numbers designed to check for mistakes in input or transmission
Natural number
whole numbers used for counting
Rational number
any number that can be written as a fraction or decimal - includes all integer values
Irrational number
cannot be expressed as a ratio of two integers or as a repeating or terminating decimal - Pi or any square root of an imperfect square are considered irrational
Ordinal number
numbers that describe position or order
Number bases
the number of different digits or combination of digits and letters that a system of counting uses to represent numbers
Real number
all rational and irrational numbers
Compression
a sequence of steps that are followed to reduce file size
Lossy compression
data compression technique that results in a loss of data
Lossless compression
data compression technique in which no data is lost
Run Length Encoding (RLE)
type of lossless compression that works by specifying the number of times a character or pixel colour repeats followed by the value of the character or pixel
Dictionary-based compression
type of lossless compression that uses a dictionary to replace repeated phrases with shorter binary strings
Encryption
transformation of data from one form to another to prevent unauthorised (third) parties from being able to understand it
Plaintext
normal text that has not been encrypted
Ciphertext
data or information that has been encrypted
Cipher
encryption method or algorithm
Key
secret information to lock or unlock the encrypted message
Vernam cipher
substitution cipher in which each character is encrypted using its own key
Caesar cipher
substitution cipher that works by shifting letters of alphabet along by a given number of characters
Sampling rate
number of samples taken per second when sound is recorded
Sound sample size
file size (in bits) = sampling rate x seconds x sample resolution
Nyquist theorem
states that sampling rate has to be at least twice the highest frequency of original signal
Monophonic
just one track of sound/single transmission path
Stereophonic
contains two different channels of transmission to add impression of positioning and direction to recording
MIDI (Musical Instrument Digital Interface)
set of standards that are used to represent music in digital form
Colour depth
The number of bits used to represent the colour of a single pixel
Image resolution
number of pixels per inch or centimetre/size of a bitmapped graphic in pixels (width x height in pixels)
Bitmap images
images created using a grid of small squares called pixels
Metadata
data that describes data
Image file size
width x height x colour depth
