1.2

• when considering secondary storage, capacity, durability, access speed, portability, reliability and cost need to be taken into account
• magnetic storage:

  • relatively cheap (lower cost per gigabyte compared to solid state)
  • highest capacity
  • relatively fast access speed (slower than solid state but faster than optical)
  • not durable or portable, as it has moving parts which can be easily damaged
• solid state storage:

  • high capacity
  • highest cost per gigabyte
  • fast access speed
  • portable and durable
• optical storage:

  • optical storage is very portable
  • not durable, as easily scratched or damaged
  • slowest access speed
  • cheapest
• capacity refers to how much data it can old
• speed refers to how fast data can be read and written from it
• computers work using transistors that can be on or off. We represent being on as 1 and being off as 0
• • bit = a single 1 or 0
  • nibble = 4 bits
  • byte = 8 bits
  • kilobyte = 1000 bytes
  • megabyte = 1000 kilobytes
  • gigabyte = 1000 megabytes
  • terabyte = 1000 gigabytes
  • petabyte = 1000 terabytes
• size of an image in bits = width x height x colour depth
• size of a sound file in bits = bit depth x sample rate x duration
• size of a text file in bits = bits per character x number of bits
• in hexadecimal, A = 10
• a bitshift to the left will multiply by 2, and a bitshift to the right will divide by 2
• converting to hex is done 4 bits at a time
• how characters are represented in binary:

  • each character is assigned a unique binary code
  • and the computer stores the binary code that represents that character instead of the character
• a character set is a defined list of all the different unique binary code assigned to characters that a computer can use
• advantage of using unicode over ascii:

  • unicode has more bits available, meaning many more characters can be used because more unique binary codes are available
  • so it can store different characters from different languages allowing for worldwide communication
• how images are represented in binary in bitmap:

  • image is made of pixels
  • each colour is assigned a unique binary value
  • for each pixel a binary value for a colour is assigned
  • and these values are stored in order
• increasing the colour depth leads to:

  • an increased file size
  • a greater range of colours, so improved image quality
• how sound is represented in binary:

  • an analogue sound wave is recorded at set intervals determined by the sample rate
  • the amplitude is measured and assigned a binary value closest to it
  • these values are stored in order in a file
  • the greater the bit-depth, the more accurate the digital sound file
• a sample is measuring the amplitude of a wave and converting it into binary code
• the same rate is the number of amplitude measurements (samples) taken per second
• the bit depth is the number of bits used per sample
• metadata is data about data on an (image file), and stores additional image information
• lossy compression is a compression method which reduces file size by discarding data that isn't needed:

  • removes data permanently, so file can never be restored to the original file
  • achieves greater compression than lossy, meaning it is quicker to send, receive and takes up less space in storage
• lossless compression is a compression method which reduces file size without loosing any data:

  • no data is lost, so file can be restored to the original file
  • not all files can be compressed using lossy, so lossless can be used on those files
  • less compression is achieved
• lossy compression is used on audio, images and videos, where the fact data is being lost wont be noticed
• lossless compression is used on text files and programs, as no data from those files can be discarded