Secondary Storage

• Magnetic Disk Drive

  • made up of a stack of platters/disks spinning at very high speed
  • Data is stored magnetically in concentric rings called tracks
  • Read/Write heads on a moving arm are used to acces sectors on the disk by polarizing microscopic regions on the disk
  • Data is read 1 block at a time
  • Data is transferred from and to the disk via a cable/electrical current being passed
• Optical Memory

  Laser Technology

  • Laser head moves across the radius of the disk and the beam shines onto the surface of the disk

  Pits and Lands

  • Tiny indentations called Pits and Lands reflect the laser beam differently
  • Reflected light is interpreted into 1s and 0s representing data on the disk

  Photodetector

  • detects the variations in reflection and converts the reflected light into electrical signals

  Binary Code

  • Electrical signals are then translated into binary code, and data is stored on a single spiral track

  Optical disk spins while the laser reads, allowing for a continuous flow of data
• Two differences between RAM and secondary storage:

  RAM is volatile

  • Secondary storage is non volatile

  RAM capacities are usually lower than secondary storage capacities

  Generally the contents of RAM can be read/written faster than secondary storage as RAM is physically closer to the CPU