1.2 Memory and Storage

• Primary storage


  Connected directly to the CPU
• RAM


  Volatile, used for short-term storage
• ROM


  Non-volatile, used for permanent storage
• Secondary storage


  • Non-volatile, used for long-term storage
  • Larger than primary storage
  • Slower than primary storage
  • Used when RAM is full
• Types of secondary storage

  • Magnetic
  • Optical
  • Solid state
• Magnetic storage (hard drives)

  • Made up of a stack of magnetised metal disks that spin thousands of times per second
  • Data stored magnetically using different levels of magnetic polarity
• Optical storage (CDs, DVDs, Blu-ray)


  • Data written and read with a laser using different reflections of light
• Solid state storage (SSDs)

  • No moving parts, just electronic circuitry
  • Use flash memory
  • Reliable, large capacities
  • Not very durable, noisy
  • Portable, reliable
  • Not durable, low capacity per disc
  • Faster, more durable
  • Expensive
• Characteristics of storage types

  • Speed
  • Cost
  • Capacity
  • Durability
• Binary

  Computer uses only 1 and 0 to represent information
• Binary units

  • Bit
  • Nibble
  • Byte
  • Kilobyte
  • Megabyte
  • Gigabyte
  • Terabyte
• Hexadecimal

  Base 16 number system using digits 0-9 and A-F
• Binary shifts

  1. Left shift 1 doubles the value

  2. Right shift 1 halves the value (rounds down)
• Overflow error occurs when the result takes up more storage space than possible
• Character sets

  • ASCII - 7 bits, 128 characters
  • Extended ASCII - 8 bits, 256 characters
  • Unicode - variable bits, supports many languages
• Bitmap image

  Digital image made up of pixels
• Image resolution

  Number of pixels per inch
• Colour depth


  Bits per pixel
• Metadata

  Information about the image
• Sound sampling


  Samples taken at regular intervals
• Sample rate


  Number of samples per second (Hz)
• Bit depth

  Number of bits per sample
• Compression

  Algorithms to reduce file size
• Lossy compression


  Permanently deletes part of the file, reduces quality
• Lossy compression


  • JPG
• Lossless compression


  Represents the file more efficiently without removing any data, changes are reversible
• Lossless compression


  • PNG, PSD