Secondary Storage


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  • Secondary Storage
    • What is it?
      • Data and programs are stored pernamently on secondary storage
      • Can be used to transfer data between computers
      • Cpu cannot access programs from it directly so must be transferred to main memory first
    • Magnetic Storage
      • Magnetic storage is used in  Hard disc Drives and digital tape drives
      • Magnetic discs consist of stacks of non - removable discs coated with magnetic materials
      • Data is encoded as opposing magnetic polarities on the surface of the disc, Electromagnets in the read/write heads read and write the data
      • Very low cost, even Budget laptops can have 1tb or more
      • Very large 1-2 TB common.
      • Fast, Random Access. Can be read instantly from any part of the disc.
      • Can find and supply required data in milliseconds
      • Portablility, Durability and Reliability
        • Not very portable, knocks may cause corrupted data
        • Very durable and Reliable
    • Optical Storage
      • CDS (Compact Discs) Store 700MB
      • DVDS (Digital Versitile Discs) Store 4.7gb
      • Blu-Ray Discs store up to 50GB
      • Low Capacity
      • Slow
      • Extremely low cost
      • Portablility, Durability and reliability
        • More portable than a hard disc drive but discs are relatively large
        • Easily scratched and data can be corrupted Data cannot be overwritten. Stored data degrade over time
        • very reliable if not Scratched
    • Solid State Memory
      • Solid-State memory is made of Flash memory
        • Flash memory is Non-Volitile Storage.
        • Flash memory uses an array of transistors, transistors use 0 or 1 and are switched from one to the other
        • Data is encoded as sets of binary digits. 8 GB of solid state  requires 32 Billion transistors
      • SSDs (Solid State Drives)
        • Provide secondary storage instead of magnetic discs
      • Secure digital cards (SD cards)
        • SD cards and Micro SD cards are used in portable devices such as phones, cameras and tablets
      • USB flash drives
        • USB Flash Drives are convenient compact forms of flash memory for sharing / transfering data
      • Moderate Solid State Drive, 128-512 GB however capacity is rapidly increasing
      • Very Fast Can Access data in nano seconds
      • More expensive than magnetic Drives and  optical drives , cost is dropping rapidly
      • Portability, Durability and reliability
        • Very Portable, even fitted inside phones
        • limited number of erase/write cycles
        • very reliable

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