data representation

• what is the order of units

  -bit(smallest unit)

  -nibble(4 bits)

  -byte(8 bits)

  -kilobyte(1000 bytes)

  -megabyte(1000 kilobytes)

  -gigabyte(1000 megabytes)

  -terabyte(1000 gigabytes)

  -petabyte(1000 terabytes)
• which base is denary and what does it look like

  -base 10

  -standard number system(0,1,2,3,4,5,6...)
• which base is binary and what does it look like

  -base 2

  -10001010
• how many denary numbers can most binary numbers represent

  0-255
• what does binary addition look like


  -

  
• what is an overflow error

  -when a result of a calculation requires more bits than are in the available range
• what is an overflow error

  -when a result of a calculation requires more bits than are in the available range

  
• what can an overflow error lead to

  -loss of accuracy

  -loss of data
• what does a binary shift do

  -moves every bit in a binary number left or right a certain number of places

  -left shifts can cause overflows whilst right shifts can cause bits to 'drop off'
• what is the difference between doing binary shifts to the left or right

  -binary shifts to the left multiply by 2 for every place shifted

  -binary shifts to the right divide by 2 for every place shifted
• which base is hexadecimal and what does it look like

  -base 16

  -4D
• why is hexadecimal used

  -easier to remember large numbers in hex since far shorter than binary

  -less chance of input errors

  
• how to convert hex to denary

  example 2B:

  • multiply first digit by 16(2*16)
  • take result and add it on to second digit(32+12)
  • (2B=44)
• how to convert denary to hex

  example 44:

  • divide number by 16(44/16)
  • whole number will be first digit and remainder 2nd digit(44/16=2 r 12)
  • (44=2B)
• how to convert binary to hex

  • split binary number into nibbles/ split it into half
  • find hex value for each nibble
  • join hex value together
• how to convert hex to binary

  • find denary value for each digit
  • convert denary to binary
  • join 2 binary nibble together
• what is a character set

  collections of characters that a computer recognises from their binary representation
• what is the most commonly used charcter set for english speakers

  ASCII
• how many bits is ASCII

  7 bits it can represent 128 bits
• what characters does ASCII contain

  numbers, uppercase letters and lowercase letters with symbols and commands scattered around
• how does each ASCII character fit into 1 byte if it is 7 bits

  an extra bit(0) is added at the start of binary code
• what is unicode

  -a character set that uses multiple bytes for each character and tries to cover every single possible letter or symbol that might be written

  -the first 128 codes in unicode are the same as ASCII

  -it covers all major languages
• which formula is used to find the size of a text file

  file size= number of bits per character*number of characters
• how are images stored

  as a series of pixels
• how are most images made up of

  • bitmap images- the colour of each pixel is represented by a binary code
  • the number of colours available is related to the number of bits available
  • blavk and white images only need 1 bit for each pixel as using 2 colours only( 0 for white, 1 for black)
• how can you make a greater range of shades and colours

  increasing the number of bits available for each pixel
• what is the colour depth of an image

  number of bits used for each pixel
• how can you work out the number of colours using colour depth

  total number of colours= 2^n(where n=number of bits per pixel)
• what is the image resolution

  the number of pixels in the image
• how does a higher resolution affect the quality of an image

  higher resolution=more pixels in image=better quality
• how to calculate the file size of an image

  file size=image resolution*colourdepth=width*height*colourdepth
• how does increasing colour depth and resolution affect file size

  higher colour depth/resolution=higher file size
• what is meta data of an image file

  -the information stored in an image file that helps the computer recreate the image on screen from binary data in each pixel

  -it usually includes file format, height, width, colour depth and resolution
• how is sound stored digitally

  -sound recorded by microphone using analogue signal

  -analogue to digital converter used to convert analogue signals into digital data
• what is the process of converting analogue to digital called

  sampling
• how can digital data be improved

  taking samples more regularily
• what do we have to do in order to convert analogue recording to digital data

  -sample the amplitude of the wave at regular intervals
• what is sample rate

  how many samples you take in a second(measured in hertz)
• wha is bit depth

  number of bits available for each sample
• what is the formula for calculating the file size of a sound file

  file size= sample rate*bit depth*length