Magnetic storage, Optical storage and Solid-state memory

Magnetic storage, Optical storage and Solid-state memory

1. Data and programs are stored permanently on secondary storage devices but the CPU can't access them so the have to be transferred to the main memeory

   • The can also be used to transfer stored data between computers

2. Magnetic storage

   • Includes hard disc drives which can store large amounts of data
   • Most laptops have hard disc drives which can store about 1 terabyte
   • Hard disc drives consist of stacks of non-removable discs coated with magnetic materials
   • The discs spin and read-write heads move across the discs. Data is encoded as opposing magnetic polarities on the surface of the disc by electromagnets in the read-write heads

3. Data can be stored on secondary storage devices. The 3 main types are magnetic disks, optical disks and solid-state (flash) memory

4. Optical storage

   • Includes: Compact disks (CDs) that store 700MB, Digital versatile discs (DVDs) that store 4.7GB, and Blu-ray discs that store up to 50GB
   • An optical disc has a single spiral track which is about 5km long and runs from the inside to the outside
   • Digital data is stored along the track by etching pits onto the surface of the disc. When the light from the laser hits the lands it's reflected back to a detector but it is scattered away by the pits and no light is detected. These 2 events represent 1 and 0 respectively.
   • In a recordable CD or CD-R the disc surface is covered in a translucent dye. Light passes through and is reflected by the disc surface. When data's written a powerful laser burns the dye creating black spots that don't reflect. The reflective areas are 1s and the black spots are 0s

5. Solid-state

   • This memory type is made of NAND flash memory