Topic 2: Data

• define binary

  data represented by just two values e.g. high/low, on/off, 1/0
• define denary

  a number system made up of ten digits (0-9)
• define hexadecimal

  a base-16 number system designed to make handling long patterns of binary digits easier for humans
• define bit

  • short for binary digit
  • the smallest unit of data in a computer
  • a bit can have the value 1 or 0 corresponding to on or off
  • all the data in a computer system is represented as patterns of bits
• define byte

  a group of 8 adjacent bits that can produce 256 different binary patterns
• define unsigned binary

  unsigned binary is used to represent positive binary numbers
• define unsigned number

  a number with a non-negative value of 0 or more
• define signed binary

  signed binary is used to represent both positive and negative numbers
• define signed number

  a number that can either be positive or negative, indicated by its sign
• define analogue

  using signals or data represented by a quantity that is continuously changing
• define analogue to digital conversion (ADC)

  the process of converting an analogue sound into a digital representation
• define underflow error

  when the result of a calculation is smaller than the smallest number that the system can represent
• define overflow error

  • an error that occurs when a calculation produces a result that is greater than the computer can store
  • an overflow error will produce an inaccurate result, which if undetected will have a knock-on effect
• define two‘s complement

  • used to represent signed numbers
  • the MSB of a two’s complement number indicates whether it’s positive or negative
  • the range of values that can be represented by 8 bits in two’s complement is -128 to +127
• define one’s complement

  the one's complement of a binary number is the value obtained by inverting (flipping) all the bits in the binary representation of the number
• define bitmap

  a digital image composed of a matrix of tiny blocks of colour called picture elements (pixels)
• define ASCII

  • American Standard Code for Information Interchange
  • a 7-bit binary code used to represent text, with each character assigned a value between 0 and 127
• define pixel

  • short for pixel element
  • the smallest element of a bitmap image
  • if an image size remains constant, then the more pixels there are, the sharper and more detailed the image is
• define resolution

  • determines the size of an image when it is displayed on screen or printed on paper and is measured in pixels per inch (ppi)
  • the higher the resolution, the more detailed the image is
• define colour depth

  • the number of bits used to encode the colour of each pixel in a bitmap image
  • the more bits used, the greater the number of tones/colours that can be represented
• define amplitude

  • a measurement of the distance the wave is from the x axis at a point in time
  • humans perceive this as the loudness or the magnitude of an analogue signal
• define sampling rate

  • can also be known as sampling frequency
  • the number of samples taken per second, measured in Hertz (Hz)
  • the higher the sampling rate, the more accurately the sound will be reproduced in the file
• define bit depth

  • the number of bits used to encode a sound sample
  • increasing the number of bits used increases the accuracy of the representation
• define sampling interval

  • the time between samples measured in seconds
  • a small sample interval produces a better reproduction of the original sound but increases the size of the file
• define compression

  • reduces the size of a file by repacking or removing some of its data
  • the two types are lossy and lossless
• define lossy compression

  • some of the data is permanently removed
  • the original file cannot be fully restored when the lossy file is decompressed
• define lossless compression

  compressing a file in such a way that it can be decompressed without any loss of data
• define nibble

  • half a byte
  • a group of 4 adjacent bits that can produce 16 different bit patterns
• define transistor

  • a tiny electronic component with two discrete states: high voltage (on) and low voltage (off)
  • billions of transistors are combined in complex integrated circuits and are etched onto the surface of the silicon chips used in computer systems
• define most significant bit (MSB)

  • the leftmost bit of a binary number with the highest place value
  • in an 8-bit binary number the MSB has a weighting of 2 to the power of 7 (128)
• define least significant bit (LSB)

  the rightmost bit of a binary number with the lowest place value of 2 to the power of 0 (1)
• define logical shift

  • a binary shift, either left or right, where the cleared positions are filled with only 0s
  • used to shift unsigned binary numbers
• define binary shift

  an operation in which all the bits of a binary pattern are shifted a number of places to either the left or the right
• define character set

  a defined list of numerical character codes recognised by a computer’s hardware and software
• define sampling points


  discrete points in time at which a reading of the amplitude of the sound is taken and stored as a binary number
• define data capacity

  the amount of data that can be stored on a secondary storage device or in a computer‘s memory